--- 1/draft-ietf-mpls-ldp-01.txt 2006-02-05 00:39:46.000000000 +0100
+++ 2/draft-ietf-mpls-ldp-02.txt 2006-02-05 00:39:47.000000000 +0100
@@ -1,720 +1,780 @@
Network Working Group Loa Andersson
-Internet Draft Bay Networks Inc.
-Expiration Date: February 1999
+Internet Draft Nortel Networks Inc.
+Expiration Date: May 1999
Paul Doolan
Ennovate Networks
Nancy Feldman
IBM Corp
Andre Fredette
- Bay Networks Inc.
+ Nortel Networks Inc.
Bob Thomas
Cisco Systems, Inc.
- August 1998
+ November 1998
LDP Specification
- draft-ietf-mpls-ldp-01.txt
+ draft-ietf-mpls-ldp-02.txt
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
- munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or
+ munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
Abstract
An overview of Multi Protocol Label Switching (MPLS) is provided in
[FRAMEWORK] and a proposed architecture in [ARCH]. A fundamental
concept in MPLS is that two Label Switching Routers (LSRs) must agree
on the meaning of the labels used to forward traffic between and
through them. This common understanding is achieved by using the
- Label Distribution Protocol (LDP) referenced in [FRAMEWORK] and
- [ARCH]. This document defines the LDP protocol.
+ Label Distribution Protocol (LDP) referenced in [ARCH]. This
+ document defines the LDP protocol.
-Open Issues
+Changes from Previous Draft
- The following LDP issues are left unresolved with this version of the
- spec:
+ - This draft removes the explicit path setup mechanism from the
+ spec.
- - The loop prevention/detection mechanism to be employed by LDP.
- This spec has retained the path vector mechanism from previous
- drafts. However, draft-ohba-mpls-loop-prevention-01.txt has been
- proposed as an alternative.
+ - This draft removes loop prevention from the spec. The MPLS
+ working group will continue to evaluate and compare the two
+ leading contenders for loop prevention: loop prevention via path
+ vectors and draft-ohba-mpls-loop-prevention-01.txt. We expect
+ that one of these methods will be selected and added to a later
+ version of LDP.
- - Support for explicitly routed LSPs. The need for this feature
- has been debated at length. This spec refines the previous
- version of the spec in this area. However, there remains some
- belief in the WG that explicitly routed LSPs should be supported
- by enhancements to RSVP and not LDP.
+ - This draft retains and refines the path vector mechanism for
+ optional loop detection. In addition, it introduces an upper
+ limit on the size of path vectors.
- The support for explicitly routed LSPs in the spec is independent
- of other LDP features and could, should the WG decide to do so,
- be removed without impact on other LDP features.
+ - This draft specifies parameters for the exponential backup used
+ to throttle session setup retry attempts. It also specifies a
+ mechanism for resetting the backoff parameters in response to LSR
+ configuration changes by adding an optional parameter to the
+ Hello message.
- - Traffic engineering considerations beyond support for explicit
- routing.
+ - This draft adds Appendix "LDP Label Distribution Procedures".
- - The need for all of the FEC types (called FEC elements in this
- version of the spec, SMDs in previous versions) is being debated.
- This version of the spec defines fewer FEC types than previous
- versions.
+ - This draft adds rules for resolving differences in the Label
+ Distribution Discipline and Merge session parameters exchanged in
+ the Initialization message.
- - LDP support for multicast is not defined in this version.
+ - This draft modifies message and TLV encodings slightly by adding
+ explicit specification of LSR behavior when an LSR does not
+ recognize the message or TLV.
+
+ - This draft modifies the encodings for the Initialization and
+ Hello messages to group parameters likely to be used together and
+ to reduce message sizes. It defines some new TLVs for use with
+ these messages and eliminates some previously defined TLVs.
+
+ - This draft specifies a procedure for negotiating the maximum PDU
+ length to be used for a session.
+
+ - This draft simplifies the encodings for the Label Mapping, Label
+ Request, Label Withdraw and Label Release messages by eliminating
+ the FEC-Label Mapping, FEC-Request, and FEC-Withdraw-Release
+ TLVs.
+
+ - This draft modifies the CoS TLV by specifying that its detailed
+ definition is a subject for further study.
+
+ - This draft adds a Return Message Id optional parameter to the
+ Label Request message and a Label Request Message Id parameter to
+ the Label Mapping message to enable an LSR to match received
+ Label Mapping messages with outstanding Label Request messages.
+
+ - This draft refines support for vendor-private protocol extensions
+ and specifies support for experimental protocol extensions.
+
+ - This draft specifies optional use of the TCP MD5 Signature Option
+ to protect against the introduction of spoofed TCP segments into
+ LDP session connection streams.
+
+Open Issues
+
+ The following LDP issues are left unresolved with this version of the
+ spec:
+
+ - LDP support for CoS is not completely specified in this version.
+ Cos support will be more fully addressed in a future version.
+
+ - LDP support for multicast is not specified in this version.
Multicast support will be addressed in a future version.
- - The message and TLV encodings are likely to change in some minor
- ways in the next draft of the spec.
+ - LDP support for multipath label switching is not specified in
+ this version. Multipath support will be addressed in a future
+ version.
Table of Contents
- 1 LDP Overview ....................................... 6
- 1.1 LDP Peers .......................................... 6
- 1.2 LDP Message Exchange ............................... 6
- 1.3 LDP Error Handling ................................. 7
- 1.4 LDP Extensibility and Future Compatibility ......... 8
- 2 LDP Operation ...................................... 8
- 2.1 FEC Types .......................................... 8
- 2.2 Mapping packets to FECs ........................... 9
- 2.3 Label Spaces, Identifiers, Sessions and Transport .. 10
- 2.4 LDP Sessions between non-Directly Connected LSRs ... 11
- 2.5 LDP Discovery ..................................... 12
- 2.5.1 Basic Discovery Mechanism .......................... 12
- 2.5.2 Extended Discovery Mechanism ....................... 12
- 2.6 Establishing and Maintaining LDP Sessions .......... 13
- 2.6.1 LDP Session Establishment .......................... 13
- 2.6.2 Transport Connection Establishment ................. 13
- 2.6.3 Session Initialization ............................. 14
- 2.6.4 Initialization State Machine ....................... 16
- 2.6.5 Maintaining Hello Adjacencies ...................... 19
- 2.6.6 Maintaining LDP Sessions ........................... 19
- 2.7 Label Distribution and Management .................. 20
- 2.7.1 Label Distribution Control Mode .................... 20
- 2.7.2 Label Retention Mode ............................... 21
- 2.7.3 Label Advertisement Mode ........................... 22
- 2.8 LDP Identifiers and Next Hop Addresses ............. 22
- 2.9 Loop Detection ..................................... 22
- 2.10 Loop Prevention via Diffusion ...................... 23
- 2.11 Explicitly Routing LSPs ............................ 24
- 2.12 ERLSP State Machine ................................ 28
- 2.12.1 Loose Segment Peg LSR Transitions: ................. 29
- 2.12.2 Loose Segment Non-Peg LSR Transitions: ............. 33
- 2.12.2.1 Strict Segment Transitions ......................... 35
- 2.12.3 ERLSP Timeouts ..................................... 35
- 2.12.4 ERLSP Error Codes .................................. 35
- 3 Protocol Specification ............................. 36
- 3.1 LDP PDUs ........................................... 36
- 3.2 Type-Length-Value Encoding ......................... 37
- 3.3 Commonly Used TLVs ................................. 38
- 3.3.1 FEC TLV ............................................ 38
- 3.3.1.1 FEC Procedures ..................................... 41
- 3.3.2 Label TLVs ......................................... 41
- 3.3.2.1 Generic Label TLV .................................. 42
- 3.3.2.2 ATM Label TLV ...................................... 42
- 3.3.2.3 Frame Relay Label TLV .............................. 43
- 3.3.3 Address List TLV ................................... 43
- 3.3.4 COS TLV ............................................ 44
- 3.3.5 Hop Count TLV ...................................... 45
- 3.3.5.1 Hop Count Procedures ............................... 45
- 3.3.6 Path Vector TLV .................................... 46
- 3.3.6.1 Path Vector Procedures ............................. 46
- 3.3.7 Status TLV ......................................... 47
- 3.4 LDP Messages ....................................... 48
- 3.4.1 Notification Message ............................... 50
- 3.4.1.1 Notification Message Procedures .................... 51
- 3.4.1.2 Events Signalled by Notification Messages .......... 51
- 3.4.1.2.1 Malformed PDU or Message ........................... 52
- 3.4.1.2.2 Unknown or Malformed TLV ........................... 52
- 3.4.1.2.3 Session Hold Timer Expiration ...................... 53
- 3.4.1.2.4 Unilateral Session Shutdown ........................ 53
- 3.4.1.2.5 Initialization Message Events ...................... 53
- 3.4.1.2.6 Events Resulting From Other Messages ............... 54
- 3.4.1.2.7 Explicitly Routed LSP Setup Events ................. 54
- 3.4.1.2.8 Miscellaneous Events ............................... 54
- 3.4.2 Hello Message ...................................... 54
- 3.4.2.1 Hello Message Procedures ........................... 55
- 3.4.3 Initialization Message ............................. 57
- 3.4.3.1 Initialization Message Procedures .................. 61
- 3.4.4 KeepAlive Message .................................. 61
- 3.4.4.1 KeepAlive Message Procedures ....................... 62
- 3.4.5 Address Message .................................... 62
- 3.4.5.1 Address Message Procedures ......................... 63
- 3.4.6 Address Withdraw Message ........................... 64
- 3.4.6.1 Address Withdraw Message Procedures ................ 64
- 3.4.7 Label Mapping Message .............................. 64
- 3.4.7.1 Label Mapping Message Procedures ................... 66
- 3.4.7.1.1 Independent Control Mapping ........................ 66
- 3.4.7.1.2 Ordered Control Mapping ............................ 67
- 3.4.7.1.3 Downstream-on-Demand Label Advertisement ........... 67
- 3.4.7.1.4 Downstream Allocation Label Advertisement .......... 68
- 3.4.8 Label Request Message .............................. 68
- 3.4.8.1 Label Request Message Procedures ................... 69
- 3.4.9 Label Withdraw Message ............................. 70
- 3.4.9.1 Label Withdraw Message Procedures .................. 71
- 3.4.10 Label Release Message .............................. 72
- 3.4.10.1 Label Release Message Procedures ................... 73
- 3.4.11 Label Query Message ................................ 73
- 3.4.11.1 Label Query Message Procecures ..................... 74
- 3.4.12 Explicit Route Request Message ..................... 74
- 3.4.12.1 Explicit Route Request Procedures .................. 78
- 3.4.13 Explicit Route Response Message .................... 78
- 3.4.13.1 Explicit Route Response Procedures ................. 79
- 3.5 Messages and TLVs for Extensibility ................ 80
- 3.5.1 Procedures for Unknown Messages and TLVs ........... 80
- 3.5.1.1 Unknown Message Types .............................. 80
- 3.5.1.2 Unknown TLV in Known Message Type .................. 80
- 3.5.2 LDP Vendor-Private Extensions ...................... 81
- 3.5.2.1 LDP Vendor-Private TLV ............................. 81
- 3.5.2.2 LDP Vendor-Private Messages ........................ 82
- 3.6 TLV Summary ........................................ 83
- 3.7 Status Code Summary ................................ 84
- 4 Security ........................................... 84
- 5 Acknowledgments .................................... 84
- 6 References ......................................... 84
- 7 Author Information ................................. 85
+ 1 LDP Overview ....................................... 7
+ 1.1 LDP Peers .......................................... 7
+ 1.2 LDP Message Exchange ............................... 7
+ 1.3 LDP Message Structure .............................. 8
+ 1.4 LDP Error Handling ................................. 8
+ 1.5 LDP Extensibility and Future Compatibility ......... 9
+ 2 LDP Operation ...................................... 9
+ 2.1 FECs ............................................... 9
+ 2.2 Label Spaces, Identifiers, Sessions and Transport .. 10
+ 2.2.1 Label Spaces ....................................... 10
+ 2.2.2 LDP Identifiers .................................... 11
+ 2.2.3 LDP Sessions ....................................... 11
+ 2.2.4 LDP Transport ...................................... 11
+ 2.3 LDP Sessions between non-Directly Connected LSRs ... 12
+ 2.4 LDP Discovery ..................................... 12
+ 2.4.1 Basic Discovery Mechanism .......................... 12
+ 2.4.2 Extended Discovery Mechanism ....................... 13
+ 2.5 Establishing and Maintaining LDP Sessions .......... 14
+ 2.5.1 LDP Session Establishment .......................... 14
+ 2.5.2 Transport Connection Establishment ................. 14
+ 2.5.3 Session Initialization ............................. 15
+ 2.5.4 Initialization State Machine ....................... 17
+ 2.5.5 Maintaining Hello Adjacencies ...................... 20
+ 2.5.6 Maintaining LDP Sessions ........................... 20
+ 2.6 Label Distribution and Management .................. 21
+ 2.6.1 Label Distribution Control Mode .................... 21
+ 2.6.1.1 Independent Label Distribution Control ............. 21
+ 2.6.1.2 Ordered Label Distribution Control ................. 21
+ 2.6.2 Label Retention Mode ............................... 22
+ 2.6.2.1 Conservative Label Retention Mode .................. 22
+ 2.6.2.2 Liberal Label Retention Mode ....................... 22
+ 2.6.3 Label Advertisement Mode ........................... 23
+ 2.7 LDP Identifiers and Next Hop Addresses ............. 23
+ 2.8 Loop Detection ..................................... 24
+ 2.8.1 Label Request Message .............................. 24
+ 2.8.2 Label Mapping Message .............................. 26
+ 2.8.3 Discussion ......................................... 27
+ 3 Protocol Specification ............................. 28
+ 3.1 LDP PDUs ........................................... 28
+ 3.2 LDP Procedures ..................................... 29
+ 3.3 Type-Length-Value Encoding ......................... 30
+ 3.4 TLV Encodings for Commonly Used Parameters ......... 31
+ 3.4.1 FEC TLV ............................................ 31
+ 3.4.1.1 FEC Procedures ..................................... 34
+ 3.4.2 Label TLVs ......................................... 34
+ 3.4.2.1 Generic Label TLV .................................. 34
+ 3.4.2.2 ATM Label TLV ...................................... 34
+ 3.4.2.3 Frame Relay Label TLV .............................. 35
+ 3.4.3 Address List TLV ................................... 36
+ 3.4.4 COS TLV ............................................ 37
+ 3.4.5 Hop Count TLV ...................................... 37
+ 3.4.5.1 Hop Count Procedures ............................... 38
+ 3.4.6 Path Vector TLV .................................... 38
+ 3.4.6.1 Path Vector Procedures ............................. 39
+ 3.4.6.1.1 Label Request Path Vector .......................... 39
+ 3.4.6.1.2 Label Mapping Path Vector .......................... 40
+ 3.4.7 Status TLV ......................................... 40
+ 3.5 LDP Messages ....................................... 42
+ 3.5.1 Notification Message ............................... 44
+ 3.5.1.1 Notification Message Procedures .................... 45
+ 3.5.1.2 Events Signaled by Notification Messages ........... 45
+ 3.5.1.2.1 Malformed PDU or Message ........................... 46
+ 3.5.1.2.2 Unknown or Malformed TLV ........................... 46
+ 3.5.1.2.3 Session Hold Timer Expiration ...................... 47
+ 3.5.1.2.4 Unilateral Session Shutdown ........................ 47
+ 3.5.1.2.5 Initialization Message Events ...................... 47
+ 3.5.1.2.6 Events Resulting From Other Messages ............... 47
+ 3.5.1.2.7 Miscellaneous Events ............................... 48
+ 3.5.2 Hello Message ...................................... 48
+ 3.5.2.1 Hello Message Procedures ........................... 50
+ 3.5.3 Initialization Message ............................. 51
+ 3.5.3.1 Initialization Message Procedures .................. 58
+ 3.5.4 KeepAlive Message .................................. 59
+ 3.5.4.1 KeepAlive Message Procedures ....................... 59
+ 3.5.5 Address Message .................................... 59
+ 3.5.5.1 Address Message Procedures ......................... 60
+ 3.5.6 Address Withdraw Message ........................... 61
+ 3.5.6.1 Address Withdraw Message Procedures ................ 61
+ 3.5.7 Label Mapping Message .............................. 61
+ 3.5.7.1 Label Mapping Message Procedures ................... 63
+ 3.5.7.1.1 Independent Control Mapping ........................ 63
+ 3.5.7.1.2 Ordered Control Mapping ............................ 64
+ 3.5.7.1.3 Downstream-on-Demand Label Advertisement ........... 64
+ 3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 65
+ 3.5.8 Label Request Message .............................. 65
+ 3.5.8.1 Label Request Message Procedures ................... 66
+ 3.5.9 Label Withdraw Message ............................. 67
+ 3.5.9.1 Label Withdraw Message Procedures .................. 68
+ 3.5.10 Label Release Message .............................. 69
+ 3.5.10.1 Label Release Message Procedures ................... 70
+ 3.6 Messages and TLVs for Extensibility ................ 71
+ 3.6.1 LDP Vendor-private Extensions ...................... 71
+ 3.6.1.1 LDP Vendor-private TLVs ............................ 71
+ 3.6.1.2 LDP Vendor-private Messages ........................ 72
+ 3.6.2 LDP Experimental Extensions ........................ 74
+ 3.7 Message Summary .................................... 74
+ 3.8 TLV Summary ........................................ 75
+ 3.9 Status Code Summary ................................ 76
+ 3.10 UDP and TCP Ports .................................. 76
+ 4 Security ........................................... 77
+ 4.1 The TCP MD5 Signature Option ....................... 77
+ 4.2 LDP Use of the TCP MD5 Signature Option ............ 78
+ 5 Intellectual Property Considerations ............... 79
+ 6 Acknowledgments .................................... 79
+ 7 References ......................................... 79
+ 8 Author Information ................................. 80
+
+ Appendix.A LDP Label Distribution Procedures .................. 82
+ A.1 Handling Label Distribution Events ................. 84
+ A.1.1 Receive Label Request .............................. 85
+ A.1.2 Receive Label Mapping .............................. 88
+ A.1.3 Receive Label Release .............................. 92
+ A.1.4 Receive Label Withdraw ............................. 94
+ A.1.5 Recognize New FEC .................................. 95
+ A.1.6 Detect change in FEC next hop ...................... 98
+ A.1.7 Receive Notification / No Label Resources .......... 100
+ A.1.8 Receive Notification / No Route .................... 101
+ A.1.9 Receive Notification / Loop Detected ............... 102
+ A.1.10 Receive Notification / Label Resources Available ... 102
+ A.1.11 Detect local label resources have become available . 103
+ A.1.12 LSR decides to no longer label switch a FEC ........ 104
+ A.1.13 Timeout of deferred label request .................. 104
+ A.2 Common Label Distribution Procedures ............... 105
+ A.2.1 Send_Label ......................................... 105
+ A.2.2 Send_Label_Request ................................. 107
+ A.2.3 Send_Label_Withdraw ................................ 108
+ A.2.4 Send_Notification .................................. 108
+ A.2.5 Send_Message ....................................... 109
+ A.2.6 Check_Received_Attributes .......................... 109
+ A.2.7 Prepare_Label_Request_Attributes ................... 110
+ A.2.8 Prepare_Label_Mapping_Attributes ................... 112
1. LDP Overview
LDP is the set of procedures and messages by which Label Switched
Routers (LSRs) establish Label Switched Paths (LSPs) through a
network by mapping network-layer routing information directly to
data-link layer switched paths. These LSPs may have an endpoint at a
directly attached neighbor (comparable to IP hop-by-hop forwarding),
or may have an endpoint at a network egress node, enabling switching
via all intermediary nodes.
- LDP associates a forwarding equivalence class (FEC) [ARCH] with each
+ LDP associates a Forwarding Equivalence Class (FEC) [ARCH] with each
LSP it creates. The FEC associated with an LSP specifies which
packets are "mapped" to that LSP. LSPs are extended through a
network as each LSR "splices" incoming labels for a FEC to the
outgoing label assigned to the next hop for the given FEC.
Note that this document is written with respect to unicast routing
only. Multicast will be addressed in a future revision.
- Note that this document is written with respect to control-driven
- traffic. It describes mappings which are initiated for routes in the
- forwarding table, regardless of traffic over those routes. However,
- LDP does not preclude data-driven support.
-
1.1. LDP Peers
Two LSRs which use LDP to exchange label/stream mapping information
are known as "LDP Peers" with respect to that information and we
speak of there being an "LDP Session" between them. A single LDP
- adjacency allows each peer to learn the other's label mappings i.e.
+ session allows each peer to learn the other's label mappings; i.e.,
the protocol is bi-directional.
1.2. LDP Message Exchange
There are four categories of LDP messages:
1. Discovery messages, used to announce and maintain the presence
of an LSR in a network.
- 2. Session messages, used to establish and maintain terminate
- sessions between LSR peers.
+ 2. Session messages, used to establish, maintain, and terminate
+ sessions between LDP peers.
3. Advertisement messages, used to create, change, and delete
label mappings for FECs.
4. Notification messages, used to provide advisory information and
- to signal errors.
+ to signal error information.
- Discovery messages provide a mechanism whereby LSRs continually
- indicate their presence in a network via the Hello message. This is
- transmitted as a UDP packet to the LDP port at the `all LSR routers'
- group multicast address. When an LSR chooses to establish a session
- with an LSR learned via the hello message, it uses the LDP
- initialization procedure over TCP transport. Upon successful
+ Discovery messages provide a mechanism whereby LSRs indicate their
+ presence in a network by sending the Hello message periodically.
+ This is transmitted as a UDP packet to the LDP port at the `all
+ routers' group multicast address. When an LSR chooses to establish a
+ session with another LSR learned via the Hello message, it uses the
+ LDP initialization procedure over TCP transport. Upon successful
completion of the initialization procedure, the two LSRs are LDP
peers, and may exchange advertisement messages.
When to request a label or advertise a label mapping to a peer is
largely a local decision made by an LSR. In general, the LSR
requests a label mapping from a neighboring LSR when it needs one,
and advertises a label mapping to a neighboring LSR when it wishes
the neighbor to use a label.
Correct operation of LDP requires reliable and in order delivery of
- mappings (although there are circumstances when this second
- requirement could be relaxed). To satisfy these requirements LDP uses
- the TCP transport for adjacency, advertisement and notification
- messages.
+ messages. To satisfy these requirements LDP uses the TCP transport
+ for session, advertisement and notification messages; i.e., for
+ everything but the UDP-based discovery mechanism.
-1.3. LDP Error Handling
+1.3. LDP Message Structure
- LDP errors and other events of interest are signaled to an LSR peer
+ All LDP messages have a common structure that uses a Type-
+ Length_Value (TLV) encoding scheme; see Section "Type-Length-Value"
+ encoding. The Value part of a TLV-encoded object, or TLV for short,
+ may itself contain one or more TLVs.
+
+1.4. LDP Error Handling
+
+ LDP errors and other events of interest are signaled to an LDP peer
by notification messages.
There are two kinds of LDP notification messages:
1. Error notifications, used to signal fatal errors. If an LSR
- receives an error notification for an LDP session with a peer,
- it terminates the peer session by closing the TCP transport
+ receives an error notification from a peer for an LDP session,
+ it terminates the LDP session by closing the TCP transport
connection for the session and discarding all label mappings
learned via the session.
2. Advisory notifications, used to pass an LSR information about
the LDP session or the status of some previous message received
from the peer.
-1.4. LDP Extensibility and Future Compatibility
+1.5. LDP Extensibility and Future Compatibility
- It is likely that functionality will be added to LDP after its
- initial release. It is also likely that this additional
- functionality will utilize new messages and object types (TLVs). It
- may be desirable to employ such new messages and TLVs within a
- network using older implementations that do not recognize them.
- While it is not possible to make every future enhancement backwards
- compatible, some prior planning can ease the introduction of new
- capabilities. This specification defines rules for handling unknown
- message types and unknown TLVs for this purpose.
+ Functionality may be added to LDP in the future. It is likely that
+ future functionality will utilize new messages and object types
+ (TLVs). It may be desirable to employ such new messages and TLVs
+ within a network using older implementations that do not recognize
+ them. While it is not possible to make every future enhancement
+ backwards compatible, some prior planning can ease the introduction
+ of new capabilities. This specification defines rules for handling
+ unknown message types and unknown TLVs for this purpose.
2. LDP Operation
-2.1. FEC Types
-
- It is necessary to precisely define which IP packets may be mapped to
- each LSP. This is done by providing a FEC specification for each LSP.
- The FEC defines which IP packets may be mapped to the same LSP, using
- a unique label.
+2.1. FECs
- LDP supports LSP granularity ranging from end-to-end flows to the
- aggregation of all traffic through a common egress node; the choice
- of granularity is determined by the FEC choice.
+ It is necessary to precisely specify which IP packets may be mapped
+ to each LSP. This is done by providing a FEC specification for each
+ LSP. The FEC identifies the set of IP packets which may be mapped to
+ that LSP.
- Each FEC is specified as a list of one or more FEC elements. Each FEC
- element specifies a set of IP packets which may be mapped to the
- corresponding LSP.
+ Each FEC is specified as a set of one or more FEC elements. Each FEC
+ element identifies a set of IP packets which may be mapped to the
+ corresponding LSP. When an LSP is shared by multiple FEC elements,
+ that LSP is terminated at (or before) the node where the FEC elements
+ can no longer share the same path.
Following are the currently defined types of FEC elements. New
element types may be added as needed:
- 1. IP Address Prefix.
-
- This element provides a list of one or more IP address
- prefixes. Any IP packet whose destination address matches one
- or more of the specified prefixes may be forwarded using the
- associated LSP.
-
- 2. Router ID
-
- This element provides a Router ID (ie, a 32 bit IP address of a
- router). Any IP packet for which the path to the destination is
- known to traverse the specified router may be forwarded using
- the associated LSP. This element allows the full set of
- destinations reachable via a specified router to be indicated
- in a single FEC element.
+ 1. IP Address Prefix. This element is an IP address prefix of any
+ length from 0 to 32 bits, inclusive.
- 3. Flow
+ 2. Host Address. This element is a 32-bit IP address.
- This element specifies a set of datagram information, such as
- port, dest-addr, src-addr, etc. This element provides LDP with
- the ability to support MPLS flows with no aggregation.
+ We say that a particular IP address "matches" a particular IP address
+ prefix if and only if that address begins with that prefix. We also
+ say that a particular packet matches a particular LSP if and only if
+ that LSP has an IP Address Prefix FEC element which matches the
+ packet's IP destination address. With respect to a particular packet
+ and a particular LSP, we refer to any IP Address Prefix FEC element
+ which matches the packet as the "matching prefix".
- Where a packet maps to more than one FEC it is transmitted on the LSP
- associated with the FEC to which the packet has the 'most specific'
- match.
+ The procedure for mapping a particular packet to a particular LSP
+ uses the following rules. Each rule is applied in turn until the
+ packet can be mapped to an LSP.
-2.2. Mapping packets to FECs
+ - If there is exactly one LSP which has a Host Address FEC element
+ that is identical to the packet's IP destination address, then
+ the packet is mapped to that LSP.
- FEC objects (TLVs) are transmitted in the LDP messages that deal with
- (advertise, request, release ad withdraw) FEC-Label mappings.
+ - If there multiple LSPs, each containing a Host Address FEC
+ element that is identical to the packet's IP destination address,
+ then the packet is mapped to one of those LSPs. The procedure
+ for selecting one of those LSPs is beyond the scope of this
+ document.
- A stream of packets with a given destination network can be
- characterized by a single Address Prefix FEC Element. This results
- in each specified address prefix sustaining its own LSP tree. This
- singular mapping is recommended in environments where little or no
- aggregation information is provided by the routing protocols (such as
- within a simple IGP), or in networks where the number of destination
- prefixes is limited.
+ - If a packet matches exactly one LSP, the packet is mapped to that
+ LSP.
- In environments where additional aggregation not provided by the
- routing protocols is desired, an aggregation list may be created. In
- this, all prefixes that are to share a common egress point may be
- advertised within the same FEC. This type of aggregation is
- configured.
+ - If a packet matches multiple LSPs, it is mapped to the LSP whose
+ matching prefix is the longest. If there is no one LSP whose
+ matching prefix is longest, the packet is mapped to one of those
+ LSPs. The procedure for selecting one of those LSPs is beyond
+ the scope of this document.
- The router ID FEC type may be used in any environment in which the
- routing protocols allow routers to determine the egress point for
- specific IP packets. For example, the router ID FEC type may be used
- in combination with BGP, OSPF, and/or IS-IS.
+ - If it is known that a packet must traverse a particular egress
+ router, and there is an LSP which has an IP Address Prefix FEC
+ element (of length 32 bits) which is an address of that router,
+ then the packet is mapped to that LSP. The procedure for
+ obtaining this knowledge is beyond the scope of this document.
- For example, the mapping between IP packets and the router ID may be
- provided via the BGP NEXT_HOP attribute. When a BGP border LSR
- injects routes into the BGP mesh, it may use its own IP address or
- the address of its external BGP peer as the value of the NEXT_HOP
- attribute. If the BGP border ISR uses its own IP address as the
- NEXT_HOP attribute, then one LSP is created which terminates at the
- BGP border, and the border LSR will forward traffic at layer-3
- towards its external BGP neighbors. If the BGP border LSR uses the
- external BGP peer as the NEXT_HOP attribute, then a separate LSP may
- be created for each external BGP neighbor, thereby allowing the
- border LSR to switch traffic directly to each of its external BGP
- neighbors.
+2.2. Label Spaces, Identifiers, Sessions and Transport
- Similarly, the mapping between IP packet and router ID may be
- provided by OSPF. This is comprised of the Router ID of the router
- that initiated the link state advertisement. The Router ID may also
- be the OSPF Area Border Router.
+2.2.1. Label Spaces
- Note that BGP and OSPF may share the same LSP when a given Router ID
- is found in both protocol's Routing Information Base.
+ The notion of "label space" is useful for discussing the assignment
+ and distribution of labels. There are two types of label spaces:
- The Router ID FEC allows aggregation of multiple IP address prefixes
- to the same LSP, without requiring that the prefixes be explicitly
- listed in the FEC. Also, it allows addresses advertised using OSPF
- and addresses advertised using BGP to be aggregated using the same
- LSP. Finally, when the set of addresses reachable via a router
- changes, and the changes are announced into the routing protocol
- (BGP, OSPF, and/or IS-IS), use of the routerID FEC eliminates the
- need to explicitly announce the route changes into LDP.
+ - Per interface label space. Interface-specific incoming labels
+ are used for interfaces that use interface resources for labels.
+ An example of such an interface is a label-controlled ATM
+ interface that uses VCIs as labels, or a Frame Relay interface
+ that uses DLCIs as labels.
-2.3. Label Spaces, Identifiers, Sessions and Transport
+ Note that the use of a per interface label space only makes sense
+ when the LDP peers are "directly connected" over an interface,
+ and the label is only going to be used for traffic sent over that
+ interface.
- The notion of "label space" is useful for discussing the assignment
- and distribution of labels. There are two types of label spaces:
+ - Per platform label space. Platform-wide incoming labels are used
+ for interfaces that can share the same labels.
- - Per interface label space. Interface-specific incoming
- labels are used for interfaces that use interface resources
- for labels. An example of such an interface is a label-
- controlled ATM interface which uses VCIs as labels, or a
- frame Relay interface which uses DLCIs as labels.
+2.2.2. LDP Identifiers
- Note that the use of a per interface label space only makes
- sense when the LDP peers are "directly connected" over an
- interface, and the label is only going to be used for
- traffic sent over that interface.
+ An LDP identifier is a six octet quantity used to identify an LSR
+ label space. The first four octets encode an IP address assigned to
+ the LSR, and the last two octets identify a specific label space
+ within the LSR. The last two octets of LDP Identifiers for
+ platform-wide label spaces are always both zero. This document uses
+ the following print representation for LDP Identifiers:
- - Per platform label space. Platform-wide incoming labels are
- used for interfaces that can share the same labels.
+ :
- An LDP identifier is a six octet quantity used to identify an
- LSR label space. The first four octets encode an IP address
- assigned to the LSR, and the last two octets identify a specific
- label space within the LSR. The last two octets of LDP Identif-
- iers for platform-wide label spaces are always both zero. This
- document uses the following print representation for LDP Iden-
- tifiers:
+ e.g., 171.32.27.28:0, 192.0.3.5:2.
- :
+ Note that an LSR that manages and advertises multiple label spaces
+ uses a different LDP Identifier for each such label space.
- for example, 171.32.27.28:0, 192.0.3.5:2.
+ A situation where an LSR would need to advertise more than one label
+ space to a peer and hence use more than one LDP Identifier occurs
+ when the LSR has two links to the peer and both are ATM (and use per
+ interface labels). Another situation would be where the LSR had two
+ links to the peer, one of which is ethernet (and uses per platform
+ labels) and the other of which is ATM.
- Note that an LSR that manages and advertises more than one label
- space uses a different LDP Identifier for each such label space.
+2.2.3. LDP Sessions
- A situation where an LSR would need to advertise more than one
- label space to a peer and hence use more than one LDP Identifier
- occurs when the LSR has two links to the peer and both are ATM
- (and use per interface labels). Another situation would be
- where the LSR had two links to the peer, one of which is ether-
- net (and uses per platform lables) and the other of which is
- ATM.
+ LDP sessions exist between LSRs to support label exchange between
+ them.
- LDP sessions exist between LSRs to support label exchange
- between them.
+ When an LSR uses LDP to advertise more than one label space to
+ another LSR it uses a separate LDP session for each label space.
- When a LSR must use LDP to advertise more than one label
- space to another LSR it uses a separate LDP session for each
- label space rather than a single LDP session for all the
- label spaces.
+2.2.4. LDP Transport
LDP uses TCP as a reliable transport for sessions.
- When multiple LDP sessions are required between two platforms
- there is one LDP session per TCP connection rather than many
- LDP sessions per TCP connection.
+ When multiple LDP sessions are required between two LSRs there is
+ one TCP session for each LDP session.
-2.4. LDP Sessions between non-Directly Connected LSRs
+2.3. LDP Sessions between non-Directly Connected LSRs
LDP sessions between LSRs that are not directly connected at the link
level may be desirable in some situations.
- For example, consider a "traffic engineering" application where LSR
- LSR1 sends traffic matching some criteria via an LSP to non-directly
- connected LSR LSR2 rather than forwarding the traffic along its nor-
- mally routed path.
+ For example, consider a "traffic engineering" application where LSRa
+ sends traffic matching some criteria via an LSP to non-directly
+ connected LSRb rather than forwarding the traffic along its normally
+ routed path.
- An LDP session between LSR1 and LSR2 enables LSR2 to label switch
- traffic arriving on the LSP from LSR1. In this situation LSR1
- applies two labels to traffic it forwards on the LSP. First, it adds
- the label learned via the LDP session with LSR2 to the packet label
- stack (either by replacing the label on top of the packet label stack
- with it if the packet arrives labeled or by pushing it if the packet
- arrives unlabeled). Next, it pushes the label for the LSP onto the
- label stack.
+ The path between LSRa and LSRb would include one or more intermediate
+ LSRs (LSR1,...LSRn). An LDP session between LSRa and LSRb would
+ enable LSRb to label switch traffic arriving on the LSP from LSRa by
+ providing LSRb means to advertise labels for this purpose to LSRa.
-2.5. LDP Discovery
+ In this situation LSRa would apply two labels to traffic it forwards
+ on the LSP to LSRb: a label learned from LSR1 to forward traffic
+ along the LSP path from LSRa to LSRb; and a label learned from LSRb
+ to enable LSRb to label switch traffic arriving on the LSP.
- LDP discovery is a mechanism that enables an LSR to discover poten-
- tial LDP peers. Discovery makes it unnecessary to explicitly config-
- ure an LSR's label switching peers.
+ LSRa first adds the label learned via its LDP session with LSRb to
+ the packet label stack (either by replacing the label on top of the
+ packet label stack with it if the packet arrives labeled or by
+ pushing it if the packet arrives unlabeled). Next, it pushes the
+ label for the LSP learned from LSR1 onto the label stack.
+
+2.4. LDP Discovery
+
+ LDP discovery is a mechanism that enables an LSR to discover
+ potential LDP peers. Discovery makes it unnecessary to explicitly
+ configure an LSR's label switching peers.
There are two variants of the discovery mechanism:
- - A basic discovery mechanism used to discover LSR neighbors
- that are directly connected at the link level.
+ - A basic discovery mechanism used to discover LSR neighbors that
+ are directly connected at the link level.
- - An extended discovery mechanism used to locate LSRs that are
- not directly connected at the link level.
+ - An extended discovery mechanism used to locate LSRs that are not
+ directly connected at the link level.
-2.5.1. Basic Discovery Mechanism
+2.4.1. Basic Discovery Mechanism
To engage in LDP Basic Discovery on an interface an LSR periodically
sends LDP Link Hellos out the interface. LDP Link Hellos are sent as
- UDP packets addressed to the well known LDP discovery port for the
+ UDP packets addressed to the well-known LDP discovery port for the
"all routers" group multicast address.
An LDP Link Hello sent by an LSR carries the LDP Identifier for the
label space the LSR intends to use for the interface and possibly
additional information.
Receipt of an LDP Link Hello on an interface identifies a "Hello
adjacency" with a potential LDP peer reachable at the link level on
the interface as well as the label space the peer intends to use for
the interface.
-2.5.2. Extended Discovery Mechanism
+2.4.2. Extended Discovery Mechanism
LDP sessions between non-directly connected LSRs are supported by LDP
Extended Discovery.
To engage in LDP Extended Discovery an LSR periodically sends LDP
Targeted Hellos to a specific IP address. LDP Targeted Hellos are
- sent as UDP packets addressed to the well known LDP discovery port at
+ sent as UDP packets addressed to the well-known LDP discovery port at
the specific address.
An LDP Targeted Hello sent by an LSR carries the LDP Identifier for
the label space the LSR intends to use and possibly additional
optional information.
Extended Discovery differs from Basic Discovery in the following
ways:
- - A Targeted Hello is sent to a specific IP address rather than
- to the "all routers" group multicast address for the outgoing
+ - A Targeted Hello is sent to a specific IP address rather than to
+ the "all routers" group multicast address for the outgoing
interface.
- - Unlike Basic Discovery, which is symmetric, Extended Discovery
- is asymmetric.
+ - Unlike Basic Discovery, which is symmetric, Extended Discovery is
+ asymmetric.
- One LSR initiates Extended Discovery with another targeted
- LSR, and the targeted LSR decides whether to respond to or
- ignore the Targeted Hello. A targeted LSR that chooses to
- respond does so by periodically sending Targeted Hellos to the
- initiating LSR.
+ One LSR initiates Extended Discovery with another targeted LSR,
+ and the targeted LSR decides whether to respond to or ignore the
+ Targeted Hello. A targeted LSR that chooses to respond does so
+ by periodically sending Targeted Hellos to the initiating LSR.
- Receipt of an LDP Targeted Hello identifies a "Hello adjacency"
- with a potential LDP peer reachable at the network level and the
- label space the peer intends to use.
+ Receipt of an LDP Targeted Hello identifies a "Hello adjacency" with
+ a potential LDP peer reachable at the network level and the label
+ space the peer intends to use.
-2.6. Establishing and Maintaining LDP Sessions
+2.5. Establishing and Maintaining LDP Sessions
-2.6.1. LDP Session Establishment
+2.5.1. LDP Session Establishment
The exchange of LDP Discovery Hellos between two LSRs triggers LDP
session establishment. Session establishment is a two step process:
- Transport connection establishment.
- Session initialization
The following describes establishment of an LDP session between LSRs
LSR1 and LSR2 from LSR1's point of view. It assumes the exchange of
Hellos specifying label space LSR1:a for LSR1 and label space LSR2:b
for LSR2.
-2.6.2. Transport Connection Establishment
+2.5.2. Transport Connection Establishment
- The exchange of Hellos results in a Hello adjacency at LSR1 which
- binds the link (L) and the label spaces LSR1:a and LSR2:b.
+ The exchange of Hellos results in the creation of a Hello adjacency
+ at LSR1 that serves to bind the link (L) and the label spaces LSR1:a
+ and LSR2:b.
1. If LSR1 does not already have an LDP session for the exchange
- of label spaces LSR1:a and LSR2:b it attempts to open an LDP
- TCP connection for a new session with LSR2.
+ of label spaces LSR1:a and LSR2:b it attempts to open a TCP
+ connection for a new LDP session with LSR2.
LSR1 determines the transport addresses to be used at its end
- (A1) and LSR2's end (A2) of the LDP TCP connection. Address
- A1 is determined as follows:
+ (A1) and LSR2's end (A2) of the LDP TCP connection. Address A1
+ is determined as follows:
- a) If LSR1 uses the Transport Address optional object to
- specify an address, A1 is the address LSR1 advertises via
- the optional object;
+ a. If LSR1 uses the Transport Address optional object (TLV) in
+ Hello's it sends to LSR2 to advertise an address, A1 is the
+ address LSR1 advertises via the optional object;
- b) If LSR1 does not use the Transport Address optional
- object, A1 is the source IP address used for Hellos to
+ b. If LSR1 does not use the Transport Address optional object,
+ A1 is the source IP address used in Hellos it sends to
LSR2.
Similarly, address A2 is determined as follows:
- a) If LSR2 uses the Transport Address optional object (TLV),
- A2 is the address LSR2 advertises via the optional
- object;
+ a. If LSR2 uses the Transport Address optional object, A2 is
+ the address LSR2 advertises via the optional object;
- b) If LSR2 does not use the Transport Address optional
- object, A2 is the source IP address used for Hellos from
- LSR2.
+ b. If LSR2 does not use the Transport Address optional object,
+ A2 is the source IP address in Hellos received from LSR2.
- 2. LSR1 determines whether it will play the active or passive
- role in session establishment by comparing addresses A1 and A2
- as unsigned integers. If A1 > A2, LSR1 plays the active role;
+ 2. LSR1 determines whether it will play the active or passive role
+ in session establishment by comparing addresses A1 and A2 as
+ unsigned integers. If A1 > A2, LSR1 plays the active role;
otherwise it is passive.
- 3. If LSR1 is active, it attempts to establish the LDP TCP con-
- nection by connecting to the well known LDP port at address
- A2. If LSR1 is passive, it waits for LSR2 to establish the
- LDP TCP connection to its well known LDP port.
+ 3. If LSR1 is active, it attempts to establish the LDP TCP
+ connection by connecting to the well-known LDP port at address
+ A2. If LSR1 is passive, it waits for LSR2 to establish the LDP
+ TCP connection to its well-known LDP port.
-2.6.3. Session Initialization
+2.5.3. Session Initialization
After LSR1 and LSR2 establish a transport connection they negotiate
session parameters by exchanging LDP Initialization messages. The
- parameters negotiated include LDP protocol version, label distribu-
- tion method, timer values, VPI/VCI ranges for label controlled ATM,
- DLCI ranges for label controlled Frame Relay, etc.
+ parameters negotiated include LDP protocol version, label
+ distribution method, timer values, VPI/VCI ranges for label
+ controlled ATM, DLCI ranges for label controlled Frame Relay, etc.
Successful negotiation completes establishment of an LDP session
between LSR1 and LSR2 for the advertisement of label spaces LSR1:a
and LSR2:b.
The following describes the session initialization from LSR1's point
of view.
- 1. After the connection is established, if LSR1 is playing the
- active role, it initiates negotiation of session parameters by
- sending an Initialization message to LSR2. If LSR1 is
- passive, it waits for LSR2 to initiate the parameter negotia-
- tion.
+ After the connection is established, if LSR1 is playing the active
+ role, it initiates negotiation of session parameters by sending an
+ Initialization message to LSR2. If LSR1 is passive, it waits for
+ LSR2 to initiate the parameter negotiation.
- In general when there are multiple links between LSR1 and LSR2
- and multiple label spaces to be advertised by each, the pas-
- sive LSR cannot know which label space to advertise over a
- newly established TCP connection until it receives the first
- LDP PDU on the connection.
+ In general when there are multiple links between LSR1 and LSR2 and
+ multiple label spaces to be advertised by each, the passive LSR
+ cannot know which label space to advertise over a newly established
+ TCP connection until it receives the first LDP PDU on the connection.
- By waiting for the Initialization message from its peer the
- passive LSR can match the label space to be advertised by the
- peer (as determined from the LDP Identifier in the common
- header for the Initialization message) with a Hello adjacency
- previously created when Hellos were exchanged.
+ By waiting for the Initialization message from its peer the passive
+ LSR can match the label space to be advertised by the peer (as
+ determined from the LDP Identifier in the PDU header for the
+ Initialization message) with a Hello adjacency previously created
+ when Hellos were exchanged.
- 2. When LSR1 plays the passive role:
+ 1. When LSR1 plays the passive role:
- a) If LSR1 receives an Initialization message it attempts to
- match the LDP Identifier carried by the message PDU with
- a Hello adjacency.
+ a. If LSR1 receives an Initialization message it attempts to
+ match the LDP Identifier carried by the message PDU with a
+ Hello adjacency.
- b) If there is a matching Hello adjacency, the adjacency
+ b. If there is a matching Hello adjacency, the adjacency
specifies the local label space for the session.
- Next LSR1 checks whether the session parameters proposed
- in the message are acceptable. If they are, LSR1 replies
- with an Initialization message of its own to propose the
+ Next LSR1 checks whether the session parameters proposed in
+ the message are acceptable. If they are, LSR1 replies with
+ an Initialization message of its own to propose the
parameters it wishes to use and a KeepAlive message to
- signal acceptance of LSR2's parameters. If the parame-
- ters are not acceptable, LSR1 responds by sending a Nak
- message and closing the TCP connection.
+ signal acceptance of LSR2's parameters. If the parameters
+ are not acceptable, LSR1 responds by sending a Session
+ Rejected/Parameters Error Notification message and closing
+ the TCP connection.
- c) If LSR1 cannot find a matching Hello adjacency it sends a
- Nak message and closes the TCP connection.
+ c. If LSR1 cannot find a matching Hello adjacency it sends a
+ Session Rejected/No Hello Error Notification message and
+ closes the TCP connection.
- d) If LSR1 receives a KeepAlive in response to its Initiali-
- zation message, the session is operational from LSR1's
- point of view.
+ d. If LSR1 receives a KeepAlive in response to its
+ Initialization message, the session is operational from
+ LSR1's point of view.
- e) If LSR1 receives a Nak message, LSR2 has rejected its
- proposed session parameters and LSR1 closes the TCP con-
- nection.
+ e. If LSR1 receives an Error Notification message, LSR2 has
+ rejected its proposed session and LSR1 closes the TCP
+ connection.
- 3. When LSR1 plays the active role:
+ 2. When LSR1 plays the active role:
- a) If LSR1 receives a Nak message, LSR2 has rejected its
- proposed session parameters and LSR1 closes the TCP con-
- nection.
+ a. If LSR1 receives an Error Notification message, LSR2 has
+ rejected its proposed session and LSR1 closes the TCP
+ connection.
- b) If LSR1 receives an Initialization message, it checks
+ b. If LSR1 receives an Initialization message, it checks
whether the session parameters are acceptable. If so, it
- replies with a KeepAlive message. If the session parame-
- ters are unacceptable, LSR1 sends a Nak message and
- closes the connection.
+ replies with a KeepAlive message. If the session
+ parameters are unacceptable, LSR1 sends a Session
+ Rejected/Parameters Error Notification message and closes
+ the connection.
- c) If LSR1 receives a KeepAlive message, LSR2 has accepted
- its proposed session parameters.
+ c. If LSR1 receives a KeepAlive message, LSR2 has accepted its
+ proposed session parameters.
- d) When LSR1 has received both an acceptable Initialization
- message and a KeepAlive message the session is opera-
- tional from LSR1's point of view.
+ d. When LSR1 has received both an acceptable Initialization
+ message and a KeepAlive message the session is operational
+ from LSR1's point of view.
It is possible for a pair of incompatibly configured LSRs that
- disagree on session parameters to engage in an endless sequence of
- messages as each Naks the other's Initialization messages. An LSR
- must throttle its session setup retry attempts with an exponential
- backoff in situations where Initialization messages are being
- Nak'd. It is also recommended that an LSR detecting such a situa-
- tion take action to notify an operator.
+ disagree on session parameters to engage in an endless sequence
+ of messages as each NAKs the other's Initialization messages with
+ Error Notification messages.
-2.6.4. Initialization State Machine
+ An LSR must throttle its session setup retry attempts with an
+ exponential backoff in situations where Initialization messages
+ are being NAK'd. It is also recommended that an LSR detecting
+ such a situation take action to notify an operator.
+
+ The session establishment setup attempt following a NAK'd
+ Initialization message must be delayed no less than 15 seconds,
+ and subsequent delays must grow to a maximum delay of no less
+ than 2 minutes. The specific session establishment action that
+ must be delayed is the attempt to open the session transport
+ connection by the LSR playing the active role.
+
+ The throttled sequence of Initialization NAKs is unlikely to
+ cease until operator intervention reconfigures one of the LSRs.
+ After such a configuration action there is no further need to
+ throttle subsequent session establishment attempts (until their
+ initialization messages are NAK'd).
+
+ Due to the asymmetric nature of session establishment,
+ reconfiguration of the passive LSR will go unnoticed by the
+ active LSR without some further action. Section "Hello Message"
+ describes an optional mechanism an LSR can use to signal
+ potential LDP peers that it has been reconfigured.
+
+2.5.4. Initialization State Machine
It is convenient to describe LDP session negotiation behavior in
terms of a state machine. We define the LDP state machine to have
five possible states and present the behavior as a state transition
table and as a state transition diagram.
Session Initialization State Transition Table
STATE EVENT NEW STATE
NON EXISTENT Session TCP connection established INITIALIZED
established
INITIALIZED Transmit Initialization msg OPENSENT
+ (Active Role)
Receive acceptable OPENREC
Initialization msg
+ (Passive Role )
Action: Transmit Initialization
msg and KeepAlive msg
Receive Any other LDP msg NON EXISTENT
- Action: Transmit Nak msg and
- close transport connection
+ Action: Transmit Error Notification msg
+ (NAK) and close transport connection
OPENREC Receive KeepAlive msg OPERATIONAL
Receive Any other LDP msg NON EXISTENT
- Action: Transmit Nak msg and
- close transport connection
+ Action: Transmit Error Notification msg
+ (NAK) and close transport connection
OPENSENT Receive acceptable OPENREC
Initialization msg
Action: Transmit KeepAlive msg
Receive Any other LDP msg NON EXISTENT
- Action: Transmit Nak msg and
- close transport connection
+ Action: Transmit Error Notification msg
+ (NAK) and close transport connection
OPERATIONAL Receive Shutdown msg NON EXISTENT
Action: Transmit Shutdown msg and
close transport connection
Receive other LDP msgs OPERATIONAL
Timeout NON EXISTENT
Action: Transmit Shutdown msg and
close transport connection
@@ -726,1094 +786,731 @@
| | | |
| +------------+ |
| Session | ^ |
| connection | | |
| established | | Rx any LDP msg except |
| V | Init msg or Timeout |
| +-----------+ |
Rx Any other | | | |
msg or | |INITIALIZED| |
Timeout / | +---| |-+ |
- Tx Nak msg | | +-----------+ | |
+ Tx NAK msg | | +-----------+ | |
| | (Passive Role) | (Active Role) |
- | | Rx Init msg / | Tx Init msg |
+ | | Rx Acceptble | Tx Init msg |
+ | | Init msg / | |
| | Tx Init msg | |
| | Tx KeepAlive | |
| V msg V |
| +-------+ +--------+ |
| | | | | |
+---|OPENREC| |OPENSENT|----------------->|
+---| | | | Rx Any other msg |
| +-------+ +--------+ or Timeout |
- Rx KeepAlive | ^ | Tx Nak msg |
+ Rx KeepAlive | ^ | Tx NAK msg |
msg | | | |
- | | | Rx Init msg / |
+ | | | Rx Acceptable |
+ | | | Init msg / |
| +----------------+ Tx KeepAlive msg |
| |
| +-----------+ |
+----->| | |
|OPERATIONAL| |
| |---------------------------->+
+-----------+ Rx Shutdown msg
- All other | ^ or TIMEOUT /
+ All other | ^ or Timeout /
LDP msgs | | Tx Shutdown msg
| |
+---+
-2.6.5. Maintaining Hello Adjacencies
+2.5.5. Maintaining Hello Adjacencies
An LDP session with a peer has one or more Hello adjacencies.
- An LDP session has multiple Hello adjacencies when a pair of LSRs are
+ An LDP session has multiple Hello adjacencies when a pair of LSRs is
connected by multiple links that share the same label space; for
example, multiple PPP links between a pair of routers. In this
- situation the Hellos an LSR sends on each such link carries the same
+ situation the Hellos an LSR sends on each such link carry the same
LDP Identifier.
LDP includes mechanisms to monitor the necessity of an LDP session
and its Hello adjacencies.
LDP uses the regular receipt of LDP Discovery Hellos to indicate a
peer's intent to use the label space identified by the Hello. An LSR
maintains a hold timer with each Hello adjacency which it restarts
when it receives a Hello that matches the adjacency. If the timer
- expires without receipt of a matching Hello from the peer, LDP con-
- cludes that the peer no longer wishes to label switch using that
- label space for the link (or target, in the case of Targeted Hellos)
- in question or that the peer has failed, and it deletes the Hello
+ expires without receipt of a matching Hello from the peer, LDP
+ concludes that the peer no longer wishes to label switch using that
+ label space for that link (or target, in the case of Targeted Hellos)
+ or that the peer has failed. The LSR then deletes the Hello
adjacency. When the last Hello adjacency for a LDP session is
deleted, the LSR terminates the LDP session by closing the transport
connection.
-2.6.6. Maintaining LDP Sessions
+2.5.6. Maintaining LDP Sessions
- LDP includes mechanisms to monitor the integrity of the session tran-
- sport connection.
+ LDP includes mechanisms to monitor the integrity of the LDP session.
LDP uses the regular receipt of LDP PDUs on the session transport
- connection to monitor the integrity of the connection. An LSR main-
- tains a keepalive timer for each peer session which it resets when-
- ever it receives an LDP PDU from the session peer. If the keepalive
- timer expires without receipt of an LDP PDU from the peer the LSR
- concludes that the transport connection is bad or that the peer has
- failed, and it terminates the peer session by closing the transport
- connection.
+ connection to monitor the integrity of the session. An LSR maintains
+ a KeepAlive timer for each peer session which it resets whenever it
+ receives an LDP PDU from the session peer. If the KeepAlive timer
+ expires without receipt of an LDP PDU from the peer the LSR concludes
+ that the transport connection is bad or that the peer has failed, and
+ it terminates the LDP session by closing the transport connection.
- An LSR must arrange that its LDP peer sees an LDP PDU from it at
- least every keepalive time period to ensure the peer restarts the
- session keepalive timer. The LSR may send any protocol message to
- meet this requirement. In circumstances where an LSR has no other
- information to communicate to its peer, it sends a KeepAlive message.
+ After an LDP session has been established, an LSR must arrange that
+ its peer receive an LDP PDU from it at least every KeepAlive time
+ period to ensure the peer restarts the session KeepAlive timer. The
+ LSR may send any protocol message to meet this requirement. In
+ circumstances where an LSR has no other information to communicate to
+ its peer, it sends a KeepAlive message.
An LSR may choose to terminate an LDP session with a peer at any
time. Should it choose to do so, it informs the peer with a Shutdown
message.
-2.7. Label Distribution and Management
+2.6. Label Distribution and Management
-2.7.1. Label Distribution Control Mode
+ The MPLS architecture [ARCH] allows an LSR to distribute a FEC label
+ binding in response to an explicit request from another LSR. This is
+ known as Downstream On Demand label distribution. It also allows an
+ LSR to distribute label bindings to LSRs that have not explicitly
+ requested them. This is known as Downstream Unsolicited label
+ distribution.
+
+ Both of these label distribution techniques may be used in the same
+ network at the same time. However, for any given LDP session, each
+ LSR must be aware of the label distribution method used by its peer
+ in order to avoid situations where one peer using Downstream
+ Unsolicted label distribution assumes its peer is also. See Section
+ "Downstream-on-Demand label Advertisement".
+
+2.6.1. Label Distribution Control Mode
The behavior of the initial setup of LSPs is determined by whether
the LSR is operating with independent or ordered LSP control. An LSR
may support both types of control as a configurable option.
-2.7.1.1. Independent Label Distribution Control
+2.6.1.1. Independent Label Distribution Control
- When using independent LSP control, each node may advertise label
+ When using independent LSP control, each LSR may advertise label
mappings to its neighbors at any time it desires. For example, when
operating in independent Downstream-on-Demand mode, an LSR may answer
requests for label mappings immediately, without waiting for a label
mapping from the next hop. When operating in independent Downstream
- allocation mode, an LSR may advertise a label mapping for a FEC to
+ Unsolicited mode, an LSR may advertise a label mapping for a FEC to
its neighbors whenever it is prepared to label-switch that FEC.
A consequence of using independent mode is that an upstream label can
be advertised before a downstream label is received. This can result
- in unlabeled packets being sent to the downstream node.
+ in unlabeled packets being sent to the downstream LSR.
-2.7.1.2. Ordered Label Distribution Control
+2.6.1.2. Ordered Label Distribution Control
When using LSP ordered control, an LSR may initiate the transmission
- of a label mapping only for an FEC for which it has a label mapping
+ of a label mapping only for a FEC for which it has a label mapping
for the FEC next hop, or for which the LSR is the egress. For each
FEC for which the LSR is not the egress and no mapping exists, the
- LSR MUST wait until a label from a downstream LSR for is received
- before mapping the FEC and passing corresponding labels to upstream
- LSRs.
+ LSR MUST wait until a label from a downstream LSR is received before
+ mapping the FEC and passing corresponding labels to upstream LSRs.
- An LSR may be an egress for some FECs, and a non-egress for others.
+ An LSR may be an egress for some FECs and a non-egress for others.
An LSR may act as an egress LSR, with respect to a particular FEC,
under any of the following conditions:
1. The FEC refers to the LSR itself (including one of its
directly attached interfaces).
2. The next hop router for the FEC is outside of the Label
Switching Network.
- 3 FEC elements are reachable by crossing a routing domain boun-
- dary, such as another area for OSPF summary net-works, or
- another autonomous system for OSPF AS externals and BGP routes
- [rfc1583] [rfc1771].
+ 3 FEC elements are reachable by crossing a routing domain
+ boundary, such as another area for OSPF summary networks,
+ or another autonomous system for OSPF AS externals and BGP
+ routes [rfc1583] [rfc1771].
-2.7.2. Label Retention Mode
+2.6.2. Label Retention Mode
-2.7.2.1. Conservative Label Retention Mode
+2.6.2.1. Conservative Label Retention Mode
- In Downstream Allocation mode, label mapping advertisements for all
- routes may be received from all peer LSRs. When using conservative
- label retention, advertised label mappings are only retained if they
- will be used to forward packets (i.e., if they are received from a
- valid next hop according to routing). If operating in Downstream-
- on-Demand mode, label mappings will only be requested of the
- appropriate next hop LSR according to routing. Since Downstream-on-
- Demand mode is primarily used when label conservation is desired
+ In Downstream Unsolicited advertisement mode, label mapping adver-
+ tisements for all routes may be received from all peer LSRs. When
+ using conservative label retention, advertised label mappings are
+ retained only if they will be used to forward packets (i.e., if they
+ are received from a valid next hop according to routing). If operat-
+ ing in Downstream-on-Demand mode, an LSR will request label mappings
+ only from the next hop LSR according to routing. Since Downstream-
+ on-Demand mode is primarily used when label conservation is desired
(e.g., an ATM switch with limited cross connect space), it is typi-
cally used with the conservative label retention mode.
- The main advantage of the conservative mode is that the only the
- labels that are required for the forwarding of data are allocated and
- maintained. This is particularly important in LSRs where the label
- space is inherently limited, such as in an ATM switch. A disadvan-
- tage of the conservative mode is that if routing changes the next hop
- for a given destination, a new label must be obtained from the new
- next hop before labeled packets can be forwarded.
+ The main advantage of the conservative mode is that only the labels
+ that are required for the forwarding of data are allocated and main-
+ tained. This is particularly important in LSRs where the label space
+ is inherently limited, such as in an ATM switch. A disadvantage of
+ the conservative mode is that if routing changes the next hop for a
+ given destination, a new label must be obtained from the new next hop
+ before labeled packets can be forwarded.
-2.7.2.2. Liberal Label Retention Mode
+2.6.2.2. Liberal Label Retention Mode
- In Downstream Allocation mode, label mapping advertisements for all
- routes may be received from all peer LSRs. When using liberal label
- retention, advertised label mappings are retained from all next hops
- regardless of whether they are valid next hops for the advertised
- mapping. When operating in Downstream-on-Demand mode, label mappings
- are requested of all peer LSRs. Note, however, that Downstream-on-
- Demand mode is typically associated with ATM switch-based LSRs where
- the conservative approach is recommended.
+ In Downstream Unsolicited advertisement mode, label mapping adver-
+ tisements for all routes may be received from all LDP peers. When
+ using liberal label retention, every label mappings received from a
+ peer LSR is retained regardless of whether the LSR is the next hop
+ for the advertised mapping. When operating in Downstream-on-Demand
+ mode with liberal label retention, an LSR might choose to request
+ label mappings for all known prefixes from all peer LSRs. Note, how-
+ ever, that Downstream-on-Demand mode is typically used by devices
+ such as ATM switch-based LSRs for which the conservative approach is
+ recommended.
The main advantage of the liberal label retention mode is that reac-
tion to routing changes can be quick because labels already exist.
The main disadvantage of the liberal mode is that unneeded label map-
pings are distributed and maintained.
-2.7.3. Label Advertisement Mode
+2.6.3. Label Advertisement Mode
Each interface on an LSR is configured to operate in either Down-
- stream or Downstream-on-Demand allocation mode. LSRs exchange adver-
- tisement modes during initialization. The major difference between
- Downstream and Downstream-on-Demand modes is in which LSR takes
- responsibility for initiating mapping requests and mapping advertise-
- ments
+ stream Unsolicited or Downstream-on-Demand advertisement mode. LSRs
+ exchange advertisement modes during initialization. The major
+ difference between Downstream Unsolicited and Downstream-on-Demand
+ modes is in which LSR takes responsibility for initiating mapping
+ requests and mapping advertisements.
-2.8. LDP Identifiers and Next Hop Addresses
+2.7. LDP Identifiers and Next Hop Addresses
An LSR maintains learned labels in a Label Information Base (LIB).
- When operating in Downstream (as opposed to Downstream-on-Demand)
- more, the LIB entry for an address prefix associates a collection of
- (LDP Identifier, label) pairs with the prefix, one such pair for each
- peer advertising a label for the prefix.
+ When operating in Downstream Unsolicited mode, the LIB entry for an
+ address prefix associates a collection of (LDP Identifier, label)
+ pairs with the prefix, one such pair for each peer advertising a
+ label for the prefix.
When the next hop for a prefix changes the LSR must retrieve the
label advertised by the new next hop from the LIB for use in forward-
ing. To retrieve the label the LSR must be able to map the next hop
address for the prefix to an LDP Identifier.
Similarly, when the LSR learns a label for a prefix from an LDP peer,
it must be able to determine whether that peer is currently a next
hop for the prefix to determine whether it needs to start using the
newly learned label when forwarding packets that match the prefix.
To make that decision the LSR must be able to map an LDP Identifier
to the peer's addresses to check whether any are a next hop for the
prefix.
To enable LSRs to map between a peer LDP identifier and the peer's
addresses, LSRs advertise their addresses using LDP Address and With-
draw Address messages.
An LSR sends an Address message to advertise its addresses to a peer.
- An LSR sends a Withdraw Address message to withdraw previously adver-
- tised addresses from a peer
-
-2.9. Loop Detection
-
- Each LSR MUST support the configurable loop-detection option. LSRs
- perform loop detection via the LSR-path-vector object (TLV) contained
- within each Mapping and Query message. Upon receiving such a mes-
- sage, the LSR performs loop detection by verifying that its unique
- router-id is not already present in the list. If a loop is detected,
- the LSR must transmit a NAK message to the sending node, and does
- not install the mapping or propagate the message any further. In
- addition, if there is an upstream label spliced to the downstream
- label for the FEC, the LSR must unsplice the labels. On those mes-
- sages in which no loop is detected, the LSR must concatenate itself
- to the LSR-path-vector before propagating.
-
- If loop detection is desired in some portion of the network, then it
- should be turned on in ALL LSRs within that portion of the network,
- else loop detection will not operate properly.
-
-2.10. Loop Prevention via Diffusion
-
- LSR diffusion support is a configurable option, which permits an LSR
- to verify that a new routed path is loop free before installing an
- LSP on that path. An LSR which supports diffusion does not splice an
- upstream label to a new downstream label until it ensures that con-
- catenation of the upstream path with the new downstream path will be
- loop free.
-
- A LSR which detects a new next hop for an FEC transmits a Query mes-
- sage containing its unique router id to each of its upstream peers.
- An LSR that receives such a Query message processes the Query as fol-
- lows. (The following procedures are described in terms of Ack and
- Nak messages. An Ack is a Notification message signalling Success; a
- Nak is a Notification message signalling Loop Detected)
-
- o If the downstream LSR not the correct next hop for the given
- FEC, the upstream LSR responds with an Ack message, indicating
- that the downstream LSR may change to the new path.
-
- o If the downstream LSR is the correct next hop for the given
- FEC, the upstream LSR performs loop detection via the LSR-
- path-vector.
-
- o If a loop is detected, the upstream LSR responds with a Nak
- message that indicates the LSR is to be "pruned, and the LSR
- unsplices all connections for that FEC to the downstream node,
- thereby pruning itself off of the tree.
-
- o If a loop is not detected, the upstream node concatenates its
- unique router-id to the LSR-path-vector, and propagates the
- Query message to its upstream peers.
-
- o Each LSR which receives an Ack message from its upstream peer
- in response to a query message, in turn forwards the ack-
- nowledgement to the downstream LSR which sent the Query mes-
- sage.
-
- o If an LSR doesn't receive a Ack Message for a given query
- within a "reasonable" period of time, it "unsplices" the
- upstream peer that has not responded, and responds with a Nak
- message to its downstream peer, indicating the pruning of the
- upstream peer.
-
- o An LSR which receives a new Query message for an FEC before it
- has received responses from all of its upstream peers for a
- previous Query message must concatenate the old and the new
- LSR-path-vector within the new query advertisement before pro-
- pagating.
-
- o The diffusion computation continues until each upstream path
- responds with an acknowledgment. An LSR that does not have any
- upstream LDP peers must acknowledge the Query message.
-
- The LSR which began the diffusion may splice its upstream label to
- the new downstream label only after receiving an acknowledge mes-
- sage from the upstream peer.
-
- As LSR diffusion support is a configurable option, an LSR which
- does not support diffusion will never originate a Query message.
- However, these LSRs must still recognize and process the Query mes-
- sages, as described above.
-
-2.11. Explicitly Routing LSPs
-
- The need for explicit routing (ER) in MPLS has been explored else-
- where [ARCH] [FRAME]. At the MPLS WG meeting held during the Wash-
- ington IETF there was consensus that LDP should support explicit
- routing of LSPs with provision for indication of associated (forward-
- ing) priority. This section specifies mechanisms to provide that
- support, and provides a means to allow the reservation of 'resources'
- for the explicitly routed LSP.
-
- In this document we propose an end to end setup mechanism that could,
- in principal, be invoked from either end of the explicitly routed LSP
- (ERLSP). However we specify it here only for the case of initiation
- by the ingress in the belief that such a mechanism maps naturally to
- the setup in the opposite direction. We believe that the, inevit-
- able, latency associated with this (end to end) setup mechanism is
- tolerable since most of the motivations for ERLSPs, for example
- 'traffic engineering' imply that the LSPs setup in this manner will
- have a long lifetime (at least when compared to those setup in
- response to dynamic routing).
-
- We introduce objects and procedures that provide support for:
-
- - Strict and Loose explicit routing
-
- - Specification of class of service
-
- - Reservation of bandwidth
-
- - Route pinning
-
- - ERLSP preemption
-
- Only unidirectional point-to-point ERLSP is specified currently.
- The scheme can be easily extended to accommodate multipoint-to-
- point ERLSPs. The FEC object (TLV) may be used to determined which
- ERLSPs are "merged" to form a multipoint-to- point ERLSP. Alterna-
- tively, a multipoint-to-point ERLSP can be setup from the egress by
- completely specifying the multipoint- to-point tree. Also, tunnel-
- ing ERLSPs within other ERLSPs is for future study.
-
- To setup a ERLSP an LSR (that will be the 'ingress' of the LSP)
- generates an explicit request. The explicit request contains an
- explicit route object which in turn contains a sequence of explicit
- request next hop objects and a pointer to the current entry in that
- sequence. The explicit request next hop objects specify the IP
- address of the LSRs through which the ERLSP should pass. These LSR
- hops specified in the explicit route are referred to as 'peg LSRs'.
-
- An explicit request MUST specify the stream that will be associated
- with the ERLSP by inserting the appropriate FEC value in the
- request. The FEC value 'opaque tunnel' exists to support ERLSPs
- where the intermediate LSRs on the LSP need know nothing about the
- traffic flowing on the LSP.
-
- The setup mechanism for ERLSPs employs an end to end protocol.
- Individual ERLSPs are uniquely identified by an ERLSPID associated
- with them by the LSR that initiates their setup. The ERLSPID is
- generated by the ingress LSR of the LSP. The ERLSPID has another
- component called Peg ERLSPID which is generated by each peg LSR
- when the next peg LSR from itself is loosely routed. This is used
- by the intermediate LSRs to identify a loosely routed segment. The
- Peg ERLSPID is not used in a segment that is strictly routed.
- Requests travel from the 'ingress' of the LSP toward what will be
- the 'egress'. Responses indicating the status of the ERLSP request
- travel back toward the ingress of the ERLSP. ERLSPID is used in
- both Request and Response messages.
-
- The addresses specified in the next hop objects in the explicit
- route object should be those of the LSR's IP address or the incom-
- ing interfaces on the LSRs through which the LSP should pass. The
- ERLSPID, FEC, incoming interface (previous hop) and LDP identifier
- of the LSR that generated the message are all stored in an ERLSP
- control block. Here's a synopsis of the entire mechanism to
- instantiate an ERLSP:
-
- An ingress node originates a ERLSP request message. The message
- contains an unique ERLSPID, FEC object, explicit route object,
- and an optional object for resource assignment for the ERLSP.
-
- At an intermediate node the 'active' ERNH object is identified
- by the pointer in the explicit route object. On message receipt
- the pointer always points to the receiving LSR object in the
- explicit route message in case of strict routing. If a segment
- of ERLSP is loosely routed then pointer always points to the
- upstream peg LSR at all the intermediate LSRs in this segment.
- The penultimate hop to the downstream peg LSR advances the
- pointer to the next ERNH object in the list.
-
- If the ERNH objects subtype indicates 'Strict' then dependent on
- the next ERNH IP address the appropriate LDP Identifier for the
- LDP session with the next hop and the appropriate output inter-
- face are discovered (by using the information learnt from the
- address message see Section "LDP Identifiers"). The outgoing
- interface (next hop) information is also stored in the ERLSP
- control block. In the case of strict ERLSP, the neighbor MUST
- be directly adjacent to the current LSR.
-
- If the ERNH object subtype indicates 'Loose' then dependent upon
- the next ERNH IP address a next hop is selected as per the FIB
- information for the downstream peg LSR. This information is
- again maintained in the ERLSP control block. Peg LSRs are
- allowed to change the Explicit Route Object if the path to the
- next Peg LSR is selected to be 'loose'. This allows the Peg
- LSRs to select a specific path to the next Peg LSR. The default
- path to the next Peg LSR in case the segment is chosen as
- 'loose' is determined by the hop-by- hop forwarding path to the
- next Peg LSR. However, Peg LSR are allowed only to select a
- path downstream to the next Peg LSR, they cannot change paths on
- any other segment of the ERLSP.
-
- Bandwidth reservations (if any) are processed. How this hap-
- pens, i.e. the precise connection admission procedures is out-
- side the scope of the LDP specification. The admission control
- must also use the preemption value specified for the LSP in
- determining if resources are available for the LSP. If a reser-
- vation cannot be accommodated a response indicating that fact is
- returned to the previous hop. Note that the resources are only
- reserved at this time. The LSRs will commit the bandwidth with
- the labels when the response comes back from the egress LSR.
-
- If the ERLSP can be accommodated the pointer in the explicit
- request object is incremented to point at the next explicit
- request next hop object in case of strict routing and the
- request message is sent to the LDP peer discovered as described
- above. In case of loose routing, the pointer is incremented
- only if the direct next hop is the next downstream peg LSR.
-
- If an LSR finds it impossible to satisfy a Explicit request then
- an 'Explicit response' message is created indicating the reason.
- The ERLSPID from (failed) request is inserted in the message and
- it is sent to the LDP peer identified in the associated entry in
- the ERLSP control block after which the ERLSP block is freed.
-
- LSRs receiving Explicit responses indicating failure process
- them in a similar manner. They create a new Explicit request
- and copy the ERLSPID and Status from the Explicit request they
- received into it. They use the ERLSPID to obtain the appropri-
- ate ERLSP control block and thus identify the LDP peer toward
- which the 'new' Explicit response message should be sent. Hav-
- ing done that they free the ERLSP control block.
-
- When an Explicit request reaches the LSR specified in the last
- ERNH object in that request and that LSR accedes to the request
- it generates an Explicit response indicating successful setup of
- the ERLSP. The egress node also includes a label in the
- response message. The Explicit response is (reverse path) for-
- warded through the LSRs that the original Explicit request
- traversed using the mechanism described above (inspection of
- ERLSP control block). In this case, of course, the ERLSP con-
- trol block is not deleted. An intermediate LSR receiving such a
- response message allocates a new label on its incoming interface
- and creates a connection between the new and the given label in
- the message. The LSR also commits the previously reserved
- bandwidth to this connection at the appropriate scheduler(s).
- The LSR then forwards the message to its previous hop with the
- new label. When the successful response reaches the ingress LSR
- the ERLSP is declared in-service.
-
- There is also support for route pinning for loosely routed seg-
- ments. When a ERLSP is pinned the loose path is not changed
- when `better' paths become available. Once a ERLSP goes in-
- service there is protocol support to reassign resources to the
- ERLSP if required.
-
-2.12. ERLSP State Machine
-
- The ERLSP control block may contain the following information:
- - ERLSPID/Peg ERLSPID
- - State
- - FEC object
- - Flags
- o Self is Peg Node
- o Pinned path
- o Upstream segment (Strict/Loose) type
- o downstream segment (Strict/Loose) type
- - next peg node
- - preemption level
- - upstream neighbor (next hop/interface)
- - downstream neighbor (next hop/interface)
- - BW information (only at peg LSRs with loose downstream
- segment)
- - Explicit Route Object (only at peg LSRs with loose
- downstream segment)
-
- For the purpose of matching message to existing ERLSP control
- block, both the ERLSPID and Peg ERLSPID in the message are
- matched against the ones in the control block. Its only when
- both of them match that the message is considered to be for the
- matched control block, otherwise it is treated as a new ERLSP
- request. The ingress may use the ERLSPID as the peg ERLSPID.
- At the peg nodes, the control block fields ERLSPID and Previous
- Peg ERLSDID are compared because Peg ERLSPID contains the self
- assigned Peg ERLSPID. Also note that the Request message at
- Peg node is only compared for ERLSPID to select a control
- block.
-
- The state tables for peg node and non peg nodes are given
- separately. Separate state tables are used only for
- illustrative purposes. The state engines can be collapsed into
- a single state engine. Moreover, a completely strict ERLSP can
- be treated as a special case of loosely routed where every
- neighbor is a peg LSR with several of the state transitions
- optimized.
-
-2.12.1. Loose Segment Peg LSR Transitions:
-
- Peg LSRs in a loosely routed ERLSP segment are those that are expli-
- citly listed in the explicit route object as the starting or ending
- of a loose segment.
-
- State NULL
-
- Event Action New State
-
- Request Create ERLSP control block; store Response
- relevant information from the Awaited
- message into the control block;
- select a new peg ERLSPID; reserve
- BW specified in the message; obtain
- next hop (or interface) towards
- next peg LSR; propagate message
- towards the obtained next hop.
-
- If last node in the explicit route Established
- object, allocate an upstream label;
- commit BW; originate a Response
- message upstream.
-
- If unable to process request for No change
- any reason, issue a NAK message to
- the sender with appropriate error
- code.
-
- Response Send NAK message to the sender. No change
-
- Others Silently ignore event. No change
-
- State RESPONSE_AWAITED
-
- Event Action New State
-
- Response Install downstream label in Established
- message; choose an upstream label;
- connect upstream to downstream
- label; commit BW to the connection;
- propagate Response upstream with
- upstream label.
-
- If unable to process Response Null
- message for any reason then recover
- resources; originate a Nak message
- upstream; originate a Release
- message downstream; delete control
- block.
-
- Upstream Release resources; propagate Nak Null
- lost downstream; delete control block.
-
- Downstream Reassign a new Peg ERLSPID. Start Retry
- lost RETRY timer.
-
- Nak from Reassign a new Peg ERLSPID. RETRY Retry
- downstream timer.
-
- If error code in Nak is severe then Null
- propagate the Nak upstream; release
- resources; delete control block.
-
- Nak from Release resources; propagate Nak Null
- upstream downstream; delete control block.
-
- New NH If ERLSP is pinned, ignore event. Retry
- Otherwise, send a Nak downstream;
- change NH in the control block;
- reassign a new Peg ERLSPID. Start
- RETRY timer.
-
- Others Silently ignore event. No change
-
- State RETRY
-
- Event Action New State
-
- Retry Originate Request message towards Response
- Timer the next hop in the control block. Awaited
-
- New NH If ERLSP is pinned, ignore the No change
- event. Otherwise change next hop
- information in the control block.
-
- Nak from Release all resources (BW, label, Null
- upstream timer); delete control block.
-
- Upstream Release all resources (BW, label, Null
- lost timer); delete control block.
-
- Release Release all resources (BW, label, Null
- timer); delete control block.
-
- Downstream If there is a new next hop, update No change
- lost that in the control block.
-
- Otherwise, delete timer; recover Null
- resources; send Nak upstream;
- delete control block.
-
- Others Silently ignore event. No change
-
- State RECONNECT_AWAITED
-
- Event Action New State
-
- Request Make appropriate changes in the Established
- control block; make label
- connection; send a Response message
- upstream with upstream label.
-
- If unable to process Request Null
- message for any reason then send a
- Release message downstream and a
- Nak message upstream; release
- resources; delete control block.
-
- Reconnect Release resources; send Release Null
- Awaited message downstream; delete control
- Timer block.
-
- Upstream Ignore event. No change
- lost
-
- Downstream Release resources; delete control Null
- lost block.
-
- New NH Release resources; delete control Null
- block.
-
- Nak from Release resources; delete control Null
- downstream block.
-
- Others Silently ignore event. No change
-
- State ESTABLISHED
-
- Event Action New State
- Upstream Start RECONNECT_AWAITED timer. Reconnect
- lost Awaited
-
- Downstream Reassign a new Peg ERLSPID. Start Retry
- lost RETRY timer.
-
- Nak from Reassign a new Peg ERLSPID. Start Retry
- downstream RETRY timer.
-
- If error code in Nak is severe then Null
- propagate the Nak upstream; release
- resources; delete control block.
-
- Nak from Reassign a new Peg ERLSPID. Start Reconnect
- upstream RECONNECT_AWAITED timer. Awaited
+ An LSR sends a Withdraw Address message to withdraw previously
+ advertised addresses from a peer
- If error code in Nak is severe, Null
- then propagate the Nak downstream;
- release resources; delete control
- block.
+2.8. Loop Detection
- New NH If ERLSP is pinned, ignore the Retry
- event. Otherwise, send a Nak
- downstream; change next hop in
- control block; reassign a new Peg
- ERLSPID. Start RETRY timer.
+ Loop detection is a configurable option which provides a mechanism
+ for finding looping LSPs and for preventing Label Request messages
+ from looping in the presence of non-merge capable LSRs.
- Release Release resources; propagate Null
- message downstream; delete control
- block.
+ The mechanism makes use of Path Vector and Hop Count TLVs carried by
+ Label Request and Label Mapping messages. It builds on the following
+ basic properties of these TLVs:
- Others Silently ignore event. No change
+ - A Path Vector TLV contains a list of the LSRs that its containing
+ message has traversed. An LSR is identified in a Path Vector
+ list by its unique LSR Identifier (Id), which is the IP address
+ component of its LDP Identifier. When an LSR propagates a mes-
+ sage containing a Path Vector TLV it adds its LSR Id to the Path
+ Vector list. An LSR that receives a message with a Path Vector
+ that contains its LSR Id detects that the message has traversed a
+ loop. LDP supports the notion of a maximum allowable Path Vector
+ length; an LSR that detects a Path Vector has reached the maximum
+ length behaves as if the containing message has traversed a loop.
-2.12.2. Loose Segment Non-Peg LSR Transitions:
+ - A Hop Count TLV contains a count of the LSRS that the containing
+ message has traversed. When an LSR propagates a message contain-
+ ing a Hop Count TLV it increments the count. An LSR that detects
+ a Hop Count has reached a configured maximum value behaves as if
+ the containing message has traversed a loop. By convention a
+ count of 0 is interpreted to mean the hop count is unknown.
+ Incrementing an unknown hop count value results in an unknown hop
+ count value (0).
- Non-peg LSRs in a loose segment of an ERLSP are the LSRs intermediate
- to two peg LSRs and through which the loose segment is routed using
- the hop-by-hop forwarding path.
+ The following paragraphs describes LDP loop detection procedures. In
+ these paragraphs, "MUST" means "MUST if configured for loop detec-
+ tion". The paragraphs specify messages that must carry Path Vector
+ and Hop Count TLVs. Note that the Hop Count TLV and its procedures
+ are used without the Path Vector TLV in situations when loop detec-
+ tion is not configured (see [ATM]).
- State NULL
+2.8.1. Label Request Message
- Event Action New State
+ The use of the Path Vector TLV and Hop Count TLV prevent Label
+ Request messages from looping in environments that include non-merge
+ capable LSRs.
- Request Create ERLSP control block; reserve Response
- BW specified in the message; obtain Awaited
- next hop (or interface) towards
- next peg LSR; if penultimate hop to
- next peg LSR then increment pointer
- in ERNH object; propagate message
- towards the obtained next hop
+ The rules that govern use of the Hop Count TLV in Label Request
+ messages by LSR R when Loop Detection is enabled are the following:
- If unable to process request for No change
- any reason, issue a Nak message to
- the sender with appropriate error
- code.
+ - The Label Request message MUST include a Hop Count TLV.
- Response Send a Nak message to the sender. No change
+ - If R is sending the Label Request because it is a FEC ingress, it
+ MUST include a Hop Count TLV with hop count value 1.
- Others Silently ignore event. No change
+ - If R is sending the Label Request as a result of having received a
+ Label Request from an upstream LSR, and if the received Label
+ Request contains a Hop Count TLV, R MUST increment the received hop
+ count value by 1 and MUST pass the resulting value in a Hop Count
+ TLV to its next hop along with the Label Request message;
- State RESPONSE_AWAITED
+ The rules that govern use of the Path Vector TLV in Label Request
+ messages by LSR R when Loop Detection is enabled are the following:
- Event Action New State
+ - If R is sending the Label Request because it is a FEC ingress, then
+ if R is non-merge capable, it MUST include a Path Vector TLV of
+ length 1 containing its own LSR Id.
- Response Install downstream label in Established
- message; choose an upstream label;
- connect upstream to downstream
- label; commit BW to connection;
- propagate Response upstream with
- upstream label.
+ - If R is sending the Label Request as a result of having received a
+ Label Request from an upstream LSR, then if the received Label
+ Request contains a Path Vector TLV or if R is non-merge capable:
- If unable to process Response Null
- message for any reason then
- recovery resources; propagate a Nak
- message upstream; originate a
- Release message downstream; delete
- control block.
+ R MUST add its own LSR Id to the Path Vector, and MUST pass the
+ resulting Path Vector to its next hop along with the Label
+ Request message. If the Label Request contains no Path Vector
+ TLV, R MUST include a Path Vector TLV of length 1 containing
+ its own LSR Id.
- Upstream Originate a Nak message downstream; Null
- lost delete control block.
+ Note that if R receives a Label Request message for a particular FEC,
+ and R has previously sent a Label Request message for that FEC to its
+ next hop and has not yet received a reply, and if R intends to merge
+ the newly received Label Request with the existing outstanding Label
+ Request, then R does not propagate the Label Request to the next hop.
- Downstream Originate a Nak message upstream; Null
- lost delete control block.
+ If R receives a Label Request message from its next hop with a Hop
+ Count TLV which exceeds the configured maximum value, or with a Path
+ Vector TLV containing its own LSR Id or which exceeds the maximum
+ allowable length, then R detects that the Label Reqeust message has
+ traveled in a loop.
- Nak from Propagate Nak message upstream; Null
- downstream release reserved BW; delete control
- block.
+ When R detects a loop, it MUST send a Loop Detected Notification mes-
+ sage to the source of the Label Request message and drop the Label
+ Request message.
- Nak from Propagate Nak message downstream; Null
- upstream release reserved BW; delete control
- block;
+2.8.2. Label Mapping Message
- New NH If ERLSP is pinned, ignore the Null
- event. Otherwise, send Nak message
- upstream and downstream; release
- reserved BW; delete control block.
+ The use of the Path Vector TLV and Hop Count TLV in the Label Mapping
+ message provide a mechanism to find and terminate looping LSPs. When
+ an LSR receives a Label Mapping message from a next hop, the message
+ is propagated upstream as specified below until an a ingress LSR is
+ reached or a loop is found.
- Release Propagate message downstream; Null
- release resources; delete control
- block.
+ The rules that govern the use of the Hop Count TLV in Label Mapping
+ messages sent by an LSR R when Loop Detection is enabled are the fol-
+ lowing:
- Others Silently ignore event. No change
+ - R MUST include a Hop Count TLV.
- State ESTABLISHED
+ - If R is the egress, the hop count value MUST be 1.
- Event Action New State
+ - If the Label Mapping message is being sent to propagate a Label
+ Mapping message received from the next hop to an upstream peer, the
+ hop count value MUST be the result of incrementing the hop count
+ value received from the next hop.
- Upstream Send Nak message downstream; Null
- lost release resources (BW, label);
- delete control block.
+ - If the Label Mapping message is not being sent to propagate a Label
+ Mapping message, the hop count value MUST be the result of incre-
+ menting R's current knowledge of the hop count to the egress. Note
+ that the hop count to the egress will be unknown if R has not
+ received a Label Mapping message from the next hop.
- Downstream Send Nak message upstream; release Null
- lost resources; delete control block.
+ Any Label Mapping message MAY contain a Path Vector TLV. The rules
+ that govern the mandatory use of the Path Vector TLV in Label Mapping
+ messages sent by LSR R when Loop Detection is enabled are the follow-
+ ing:
- Nak from Release resources; propagate Nak Null
- downstream message upstream; delete control
- block.
+ - If R is the egress, the Label Mapping message need not include a
+ Path Vector TLV.
- Nak from Release resources; propagate Null
- upstream message Nak downstream; delete
- control block.
+ - If R is sending the Label Mapping message to propagate a Label Map-
+ ping message received from the next hop to an upstream peer, then:
- New NH If ERLSP is pinned, ignore the Null
- event. Otherwise, release
- resources; originate Nak message
- upstream; originate Nak message
- downstream; delete control block.
+ o If R is merge capable and if R has not previously sent a Label
+ Mapping message to the upstream peer, then it MUST include a
+ Path Vector TLV.
- Release Release resources; propagate Null
- message downstream; delete control
- block.
+ o If the received message contains an unknown hop count, then R
+ MUST include a Path Vector TLV.
- Others Silently ignore event. No change
+ o If R has previously sent a Label Mapping message to the
+ upstream peer, then it MUST include a Path Vector TLV if the
+ received message reports an LSP hop count increase, a change in
+ hop count from unknown to known, or a change from known to
+ unknown.
-2.12.2.1. Strict Segment Transitions
+ If the above rules require R include a Path Vector TLV in the Label
+ Mapping message, R computes it as follows:
- A LSR whose upstream and downstream segment of an ERLSP is
- strict has a state transition exactly similar to the non-peg
- LSR (only different being does not handle the case of pinned
- down option).
+ o If the received Label Mapping message included a Path Vector,
+ the Path Vector sent upstream MUST be the result of adding R's
+ LSR Id to the received Path Vector.
-2.12.3. ERLSP Timeouts
+ o If the received message had no Path Vector, the Path Vector
+ sent upstream MUST be a path vector of length 1 containing R's
+ LSR Id.
- The following timeouts are used in the state transition:
+ - If the Label Mapping message is not being sent to propagate a
+ received message upstream, the Label Mapping message MUST include a
+ Path Vector of length 1 containing R's LSR Id.
- RETRY
- Default value TBD. This timer is set by the peg LSR to ori-
- ginate a Request message downstream on the elapse of the timer
- when a downstream loose segment is lost.
+ If R receives a Label Mapping message from its next hop with a Hop
+ Count TLV which exceeds the configured maximum value, or with a Path
+ Vector TLV containing its own LSR Id or which exceeds the maximum
+ allowable length, then R detects that the corresponding LSP contains
+ a loop.
- RECONNECT
- Default value TBD. This timer is set by the peg LSR to dein-
- stall an ERLSP on the elapse of the timer when a upstream
- loose segment is lost.
+ When R detects a loop, it MUST stop using the label for forwarding,
+ drop the Label Mapping message. and send a Loop Detected Notification
+ message to the source of the Label Mapping message.
-2.12.4. ERLSP Error Codes
+2.8.3. Discussion
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ LSRs which are configured for loop detection are NOT expected to
+ store the path vectors as part of the LSP state.
- To be supplied.
+ Note that in a network where only non-merge capable LSRs are present,
+ Path Vectors are passed downstream from ingress to egress, and are
+ not passed upstream. Even when merge is supported, Path Vectors need
+ not be passed upstream along an LSP which is known to reach the
+ egress. When an LSR experiences a change of next hop, it need pass
+ Path Vectors upstream only when it cannot tell from the hop count
+ that the change of next hop does not result in a loop.
- This subsection should be moved to Section 3.
+ In the case of ordered label distribution, Label Mapping messages are
+ propagated from egress toward ingress, naturally creating the Path
+ Vector along the way. In the case of independent label distribution,
+ an LSR may originate a Label Mapping message for an FEC before
+ receiving a Label Mapping message from its downstream peer for that
+ FEC. In this case, the subsequent Label Mapping message for the FEC
+ received from the downstream peer is treated as an update to LSP
+ attributes, and the Label Mapping message must be propagated
+ upstream. Thus, it is recommended that loop detection be configured
+ in conjunction with ordered label distribution, to minimize the
+ number of Label Mapping update messages.
- END NOTE * END NOTE * END NOTE:
+ If loop detection is desired in some portion of the network, then it
+ should be turned on in ALL LSRs within that portion of the network,
+ else loop detection will not operate properly.
3. Protocol Specification
Previous sections that describe LDP operation have discussed
scenarios that involve the exchange of messages among LDP peers.
This section specifies the message encodings and procedures for pro-
cessing the messages.
LDP message exchanges are accomplished by sending LDP protocol data
units (PDUs) over LDP session TCP connections.
Each LDP PDU can carry one or more LDP messages. Note that the mes-
sages in an LDP PDU need not be related to one another. For example,
a single PDU could carry a message advertising FEC-label bindings for
several FECs, another message requesting label bindings for several
- other FECs, and a third notification message signalling some event.
+ other FECs, and a third notification message signaling some event.
3.1. LDP PDUs
- Each LDP PDU is a fixed LDP header followed by one or more LDP mes-
- sages. The fixed LDP header is:
+ Each LDP PDU is an LDP header followed by one or more LDP messages.
+ The LDP header is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LDP Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | | Res |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP protocol
version 1.
PDU Length
- Two octet integer specifying the total length of this PDU in bytes,
- excluding the Version and PDU Length fields.
+ Two octet integer specifying the total length of this PDU in
+ octets, excluding the Version and PDU Length fields.
+
+ The maximum allowable PDU Length is negotiable when an LDP session
+ is initialized. Prior to completion of the negotiation the maximum
+ allowable length is 4096 bytes.
LDP Identifier
Six octet field that uniquely identifies the label space for which
this PDU applies. The first four octets encode an IP address
assigned to the LSR. This address should be the router-id, also
- used in LSR Path Vector used by loop detection and loop prevention
- procedures. The last two octets identify a label space within the
- LSR. For a platform-wide label space, these should both be zero.
+ used to identify the LSR in loop detection Path Vectors. The last
+ two octets identify a label space within the LSR. For a platform-
+ wide label space, these should both be zero.
- Res
- This field is reserved. It must be set to zero on transmission and
- must be ignored on receipt.
+ Note that there is no alignment requirement for the first octet of an
+ LDP PDU.
-3.2. Type-Length-Value Encoding
+3.2. LDP Procedures
+
+ LDP defines messages, TLVs and procedures in the following areas:
+
+ - Peer discovery;
+ - Session management;
+ - Label distribution;
+ - Notification of errors and advisory information.
+
+ The sections that follow describe the message and TLV encodings for
+ these areas and the procedures that apply to them.
+
+ The label distribution procedures are complex and are difficult to
+ describe fully, coherently and unambiguously as a collection of
+ separate message and TLV specifications.
+
+ Appendix A, "LDP Label Distribution Procedures", describes the label
+ distribution procedures in terms of label distribution events that
+ may occur at an LSR and how the LSR must respond. Appendix A is the
+ specification of LDP label distribution procedures. If a procedure
+ described elsewhere in this document conflicts with Appendix A,
+ Appendix A specifies LDP behavior.
+
+3.3. Type-Length-Value Encoding
LDP uses a Type-Length-Value (TLV) encoding scheme to encode much of
- LDP message contents. An LDP TLV is encoded as a 2 octet Type field,
- followed by a 2 octet Length Field followed by a variable length
- Value field.
+ the information carried in LDP messages.
+
+ An LDP TLV is encoded as a 2 octet field that uses 14 bits to specify
+ a Type and 2 bits to specify behavior when an LSR doesn't recognize
+ the Type, followed by a 2 octet Length Field, followed by a variable
+ length Value field.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Type | Length |
+ |U|F| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
~ ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ U bit
+ Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
+ (=0), a notification must be returned to the message originator and
+ the entire message must be ignored; if U is set (=1), the unknown
+ TLV is silently ignored and the rest of the message is processed as
+ if the unknown TLV did not exist.
+
+ F bit
+ Forward unknown TLV bit. This bit applies only when the U bit is
+ set and the LDP message containing the unknown TLV is to be for-
+ warded. If F is clear (=0), the unknown TLV is not forwarded with
+ the containing message; if F is set (=1), the unknown TLV is for-
+ warded with the containing message.
+
Type
Encodes how the Value field is to be interpreted.
Length
Specifies the length of the Value field in octets.
Value
- Octet string of Length octets that encodes information the
- interpretation of which is specfied by the Type field.
+ Octet string of Length octets that encodes information to be inter-
+ preted as specified by the Type field.
+
+ Note that there is no alignment requirement for the first octect of a
+ TLV.
Note that the Value field itself may contain TLV encodings. That is,
TLVs may be nested.
The TLV encoding scheme is very general. In principle, everything
appearing in an LDP PDU could be encoded as a TLV. This specifica-
tion does not use the TLV scheme to its full generality. It is not
used where its generality is unnecessary and its use would waste
space unnecessarily. These are usually places where the type of a
value to be encoded is known, for example by its position in a mes-
sage or an enclosing TLV, and the length of the value is fixed or
readily derivable from the value encoding itself.
Some of the TLVs defined for LDP are similar to one another. For
example, there is a Generic Label TLV, an ATM Label TLV, and a Frame
Relay TLV; see Sections "Generic Label TLV", "ATM Label TLV", and
"Frame Relay TLV".
- While is possible to think about TLVs related in this way in terms of
- a TLV type that specifies a TLV class and a TLV subtype that speci-
- fies a particular kind of TLV within that class, this specification
- does not formalize the notion of a TLV subtype.
+ While it is possible to think about TLVs related in this way in terms
+ of a TLV type that specifies a TLV class and a TLV subtype that
+ specifies a particular kind of TLV within that class, this specifica-
+ tion does not formalize the notion of a TLV subtype.
The specification assigns type values for related TLVs, such as the
label TLVs, from of a contiguous block in the 16-bit TLV type number
space.
Section "TLV Summary" lists the TLVs defined in this version of the
- protocol and the document section that describes each.
+ protocol and the section in this document that describes each.
-3.3. Commonly Used TLVs
+3.4. TLV Encodings for Commonly Used Parameters
- There are several TLV encodings used by more than one LDP message.
- The encodings for these commonly used TLVs are specified in this sec-
- tion.
+ There are several parameters used by more than one LDP message. The
+ TLV encodings for these commonly used parameters are specified in
+ this section.
-3.3.1. FEC TLV
+3.4.1. FEC TLV
- Labels are bound to Forwarding Equivalence Classes (FECs). An FEC is
+ Labels are bound to Forwarding Equivalence Classes (FECs). a FEC is
a list of one or more FEC elements. The FEC TLV encodes FEC items.
Its encoding is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC (0x0100) | Length |
+ |U|F| FEC (0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
FEC Element 1 to FEC Element n
- There are several types of FEC elements; see Section "FEC Types".
- The FEC element encoding depends on the type of FEC element. Note
- that while the representation of the FEC element value is type-
- dependent that the value encoding itself is one where standard LDP
- TLV encoding is not used.
+ There are several types of FEC elements; see Section "FECs". The
+ FEC element encoding depends on the type of FEC element.
A FEC Element value is encoded as a 1 octet field that specifies
the element type, and a variable length field that is the type-
- dependent element value.
+ dependent element value. Note that while the representation of the
+ FEC element value is type-dependent, the FEC element encoding
+ itself is one where standard LDP TLV encoding is not used.
The FEC Element value encoding is:
FEC Element Type Value
type name
Wildcard 0x01 No value; i.e., 0 value octets;
see below.
- Prefix 0x02 See Prefix value encoding below.
- Router Id 0x03 4 octet full IP address.
- Flow 0x04 See Flow value encoding below.
+ Prefix 0x02 See below.
+ Host Address 0x03 4 octet full IP address; see below.
Wildcard FEC Element
To be used only in the Label Withdraw and Label Release Messages.
Indicates the withdraw/release is to be applied to all FECs asso-
ciated with the label within the following label TLV. Must be
the only FEC Element in the FEC TLV.
Prefix FEC Element value encoding:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Address Family | PreLen | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
- | |
+ | Prefix (2) | Address Family | PreLen |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix |
- | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family
Two octet quantity containing a value from ADDRESS FAMILY
- NUMBERS in Assigned Numbers [ref] that encodes the address fam-
- ily for the address prefix in the Prefix field.
+ NUMBERS in [rfc1700] that encodes the address family for the
+ address prefix in the Prefix field.
PreLen
One octet unsigned integer containing the length in bits of the
address prefix that follows.
Prefix
An address prefix encoded according to the Address Family
field, whose length, in bits, was specified in the PreLen
field, padded to a byte boundary.
- Flow FEC Element value encoding:
+ Host Address FEC Element encoding:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Network Source Address |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Network Destination Address |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Source Port | Dest Port |
+ | Host Addr (3) | Address Family | Host Addr Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Protocol | Direction | Reserved |
+ | |
+ | Host Addr |
+ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Network Source Address
- Four octet source IPv4 address.
-
- Network Destination Address
- Four octet destination IPv4 address.
-
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
-
- For generality the address encodings here should include an
- Address Family field, etc.
-
- END NOTE * END NOTE * END NOTE:
-
- Source Port
- Two octet source port.
-
- Destination Port
- Two octet destination port.
-
- Protocol
- Protocol type.
-
- Direction
- One octet indicating the direction of the LSP. Field is set to
- 1 on Downstream; field is set to 2 on Upstream.
-
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ Address Family
+ Two octet quantity containing a value from ADDRESS FAMILY
+ NUMBERS in [rfc1700] that encodes the address family for the
+ address prefix in the Prefix field.
- Use of this FEC is not fully specified in this version of the
- protocol
+ Host Addr Len
+ Length of the Host address in octets.
- END NOTE * END NOTE * END NOTE:
+ Host Addr
+ An address encoded according to the Address Family field.
-3.3.1.1. FEC Procedures
+3.4.1.1. FEC Procedures
If in decoding a FEC TLV an LSR encounters a FEC Element type it can-
not decode, it should stop decoding the FEC TLV, abort processing the
- message containing the TLV, and send an Ack/Nack message to its LSR
- peer signalling an error.
+ message containing the TLV, and send an Notification message to its
+ LDP peer signaling an error.
-3.3.2. Label TLVs
+3.4.2. Label TLVs
Label TLVs encode labels. Label TLVs are carried by the messages
used to advertise, request, release and withdraw label mappings.
There are several different kinds of Label TLVs which can appear in
situations that require a Label TLV.
-3.3.2.1. Generic Label TLV
+3.4.2.1. Generic Label TLV
An LSR uses Generic Label TLVs to encode labels for use on links for
which label values are independent of the underlying link technology.
Examples of such links are PPP and Ethernet.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Generic Label (0x0200) | Length |
+ |U|F| Generic Label (0x0200) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Label
This is a 20-bit label value as specified in [ENCAP] represented as
a 20-bit number in a 4 octet field.
-3.3.2.2. ATM Label TLV
+3.4.2.2. ATM Label TLV
An LSR uses ATM Label TLVs to encode labels for use on ATM links.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ATM Label (0x0201) | Length |
+ |U|F| ATM Label (0x0201) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Res| V | VPI | VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
Res
This field is reserved. It must be set to zero on transmission and
must be ignored on receipt.
V-bits
Two-bit switching indicator. If V-bits is 00, both the VPI and VCI
are significant. If V-bits is 01, only the VPI field is signifi-
cant. If V-bit is 10, only the VCI is significant.
VPI
@@ -1815,35 +1512,35 @@
Two-bit switching indicator. If V-bits is 00, both the VPI and VCI
are significant. If V-bits is 01, only the VPI field is signifi-
cant. If V-bit is 10, only the VCI is significant.
VPI
Virtual Path Identifier. If VPI is less than 12-bits it should be
right justified in this field and preceding bits should be set to
0.
VCI
- Virtual Connection Identifier. If the VCI is less than 16- bits, it
+ Virtual Channel Identifier. If the VCI is less than 16- bits, it
should be right justified in the field and the preceding bits must
be set to 0. If Virtual Path switching is indicated in the V-bits
field, then this field must be ignored by the receiver and set to 0
by the sender.
-3.3.2.3. Frame Relay Label TLV
+3.4.2.3. Frame Relay Label TLV
An LSR uses Frame Relay Label TLVs to encode labels for use on Frame
Relay links.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Frame Relay Label (0x0202) | Length |
+ |U|F| Frame Relay Label (0x0202)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res
This field is reserved. It must be set to zero on transmission and
must be ignored on receipt.
Len
This field specifies the number of bits of the DLCI. The following
@@ -1841,741 +1538,926 @@
| Reserved |Len| DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res
This field is reserved. It must be set to zero on transmission and
must be ignored on receipt.
Len
This field specifies the number of bits of the DLCI. The following
values are supported:
+
0 = 10 bits DLCI
1 = 17 bits DLCI
2 = 23 bits DLCI
-
DLCI
- The Data Link Connection Identifier. Refer to
- draft-ietf-mpls-fr-01.txt [FR] for the label values and formats.
+ The Data Link Connection Identifier. Refer to [FR] for the label
+ values and formats.
-3.3.3. Address List TLV
+3.4.3. Address List TLV
The Address List TLV appears in Address and Address Withdraw mes-
sages.
Its encoding is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Address List (0x0101) | Length |
+ |U|F| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| Addresses |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family
Two octet quantity containing a value from ADDRESS FAMILY NUMBERS
- in Assigned Numbers [ref] that encodes the addresses contained in
- the Addresses field.
+ in [rfc1700] that encodes the addresses contained in the Addresses
+ field.
Addresses
A list of addresses from the specified Address Family. The encod-
ing of the individual addresses depends on the Address Family.
The following address encodings are defined by this version of the
protocol:
Address Family Address Encoding
IPv4 4 octet full IPv4 address
-3.3.4. COS TLV
+3.4.4. COS TLV
The COS (Class of Service) TLV may appear as an optional field in
- messages that carry label mappings. Its encoding is:
+ messages that request and carry label mappings. It is used to
+ request and advertise (Label, FEC, class of service) bindings. Its
+ encoding is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | COS (0x0102) | Length |
+ |U|F| COS (0x0102) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| COS Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- COS Value
- The COS Value may be one of several types, encoded as a 1 octet
- type followed by a variable length, type-dependent value. Note
- that the encoding of the COS value is not the standard LDP TLV
- encoding. Note also that the length of the type-dependent value
- can be derived from the length of the COS TLV.
-
- The following COS value encodings are defined by this version of
- the protocol:
- COS Name Type code Value
-
- IP Prec 0x01 1 octet IP Precedence
+ COS Value
+ The value field for this TLV is a subject for further study.
- If in decoding a COS TLV an LSR encounters a COS type it cannot
- decode, it should stop decoding the COS TLV, abort processing the
- message containing the TLV, and send an Ack/Nack message to its LSR
- peer signalling an error.
+ One possibility is to define a set of CoS values that map to Dif-
+ ferentiated Services [DIFFSERV] code points. Other CoS values
+ could be supported in addition to or in place of the Differentiated
+ Services code points.
-3.3.5. Hop Count TLV
+3.4.5. Hop Count TLV
The Hop Count TLV appears as an optional field in messages that set
up LSPs. It calculates the number of LSR hops along an LSP as the
LSP is being setup.
+ Note that setup procedures for LSPs that traverse ATM links require
+ use of the Hop Count TLV (see [ATM]).
+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Hop Count (0x0103) | Length |
+ |U|F| Hop Count (0x0103) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HC Value |
+-+-+-+-+-+-+-+-+
HC Value
1 octet unsigned integer hop count value.
-3.3.5.1. Hop Count Procedures
+3.4.5.1. Hop Count Procedures
During setup of an LSP an LSR may receive a Label Mapping or Label
Request message for the LSP that contains the Hop Count TLV. If it
- does, it should record the hop count value. If the LSR then passes a
- Label Mapping message for the LSP to an upstream peer or a Label
- Request to a downstream peer to continue the LSP setup, it must
- increment the recorded hop count value and include it in a Hop Count
- TLV in the message. The first LSR in the LSP should set the hop
- count value to 1.
+ does, it should record the hop count value. If the LSR then pro-
+ pagates the Label Mapping message for the LSP to an upstream peer or
+ the Label Request message to a downstream peer to continue the LSP
+ setup, it must increment the recorded hop count value and include it
+ in a Hop Count TLV in the message. The first LSR in the LSP should
+ set the hop count value to 1.
- If an LSR receives a Label Mapping message containing a Hop Count
- TLV, it must check the hop count value to determine whether the hop
- count has wrapped (hop count value = 0). If so, it must reject the
- Label Mapping message in order to prevent a forwarding loop.
+ By convention a value of 0 indicates an unknown hop count. The
+ result of incrementing an unknown hop count is itself an unknown hop
+ count (0).
-3.3.6. Path Vector TLV
+ If an LSR receives a message containing a Hop Count TLV, it must
+ check the hop count value to determine whether the hop count has
+ exceeded its configured maximum allowable value. If so, it must
+ behave as if the containing message has traversed a loop by sending a
+ Notification message signaling Loop Detected in reply to the sender
+ of the message.
- The Path Vector TLV is used in messages that implement LDP loop
- detection and prevention. It records the path of LSRs a label adver-
- tisement has traversed to setup an LSP. Its encoding is:
+ If Loop Detection is configured, the LSR must follow the procedures
+ specified in Section "Loop Detection".
+
+3.4.6. Path Vector TLV
+
+ The Path Vector TLV is used with the Hop Count TLV in Label Request
+ and Label Mapping messages to implement the optional LDP loop detec-
+ tion mechanism. See Section "Loop Detection". Its use in the Label
+ Request message records the path of LSRs the request has traversed.
+ Its use in the Label Mapping message records the path of LSRs a label
+ advertisement has traversed to setup an LSP.
+
+ Its encoding is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Path Vector (0x0104) | Length |
+ |U|F| Path Vector (0x0104) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSR Id 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSR Id n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
One or more LSR Ids
- A list of router-identifiers indicating the path of LSRs the map-
- ping message has traversed. Each router-id must be the router-id
- component of the LDP identifier for the corresponding LSR. This
- ensures it is unique within the LSR network.
+ A list of router-ids indicating the path of LSRs the message has
+ traversed. Each LSR Id is the IP address (router-id) component of
+ the LDP identifier for the corresponding LSR. This ensures it is
+ unique within the LSR network.
-3.3.6.1. Path Vector Procedures
+3.4.6.1. Path Vector Procedures
- During setup of an LSP an LSR may receive a Label Mapping message for
- the LSP that contains the Path Vector TLV. If it does, the LSR must
- pass a Label Mapping message for the LSP to the upstream peer(s) to
- continue the LSP setup. This message must include a Path Vector TLV
- in the message. The value of the path vector in the Path Vector TLV
- must be the received path vector with the LSRs own LSR Id appended to
- it.
+ The Path Vector TLV is carried in Label Mapping and Label Request
+ messages when loop detection is configured.
- If an LSR receives a Label Mapping message containing a Path Vector
- TLV, it must check the path vector value to determine whether the
- vector contains its own LSR-id. If so, it must reject the Label Map-
- ping message in order to prevent a forwarding loop.
+3.4.6.1.1. Label Request Path Vector
- The Path Vector TLV is also used in the Label Query message. See
- Sections "Loop Detection" and "Loop Prevention via Diffusion" for
- more details.
+ Section "Loop Detection" specifies situations when an LSR must
+ include a Path Vector TLV in a Label Request message.
-3.3.7. Status TLV
+ An LSR that receives a Path Vector in a Label Request message must
+ perform the procedures described in Section "Loop Detection".
+
+ If the LSR detects a loop, it must reject the Label Request message.
+ The LSR must:
+
+ 1. Transmit a Notification message to the sending LSR signaling
+ "Loop Detected".
+
+ 2. Not propagate the Label Reqeust message further.
+
+ Note that a Label Request message with Path Vector TLV is forwarded
+ until:
+
+ 1. A loop is found,
+
+ 2. The LSP egress is reached,
+
+ 3. The maximum Path Vector limit or maximum Hop Count limit is
+ reached. This is treated as if a loop had been detected.
+
+3.4.6.1.2. Label Mapping Path Vector
+
+ Section "Loop Detection" specifies the situations when an LSR must
+ include a Path Vector TLV in a Label Mapping message.
+
+ An LSR that receives a Path Vector in a Label Mapping message must
+ perform the procedures described in Section "Loop Detection".
+
+ If the LSR detects a loop, it must reject the Label Mapping message
+ in order to prevent a forwarding loop. The LSR must:
+
+ 1. Transmit a Notification message to the sending LSR signaling
+ "Loop Detected".
+
+ 2. Not propagate the message further.
+
+ 3. Check whether the Label Mapping message is for an existing LSP.
+ If so, the LSR must unsplice any upstream labels which are
+ spliced to the downstream label for the FEC.
+
+ Note that a Label Mapping message with a Path Vector TLV is forwarded
+ until:
+
+ 1. A loop is found,
+
+ 2. An LSP ingress is reached, or
+
+ 3. The maximum Path Vector or maximum Hop Count limit is reached.
+ This is treated as if a loop had been detected.
+
+3.4.7. Status TLV
Notification messages carry Status TLVs to specify events being sig-
- nalled.
+ naled.
The encoding for the Status TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Status (0x0300) | Length |
+ |U|F| Status (0x0300) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Status Code
- 32-bit unsigned integer encoding the event being signalled. The
+ 32-bit unsigned integer encoding the event being signaled. The
structure of a Status Code is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |F|E| Status Data |
+ |E|F| Status Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- F bit
+ E bit
Fatal error bit. If set (=1), this is a fatal error notifica-
tion. If clear (=0), this is an advisory notification.
- E bit
- End-to-end bit. If set (=1), the notification should be for-
- warded to the LSR for the next-hop or previous-hop for the LSP,
- if any, associated with the event being signalled. If clear
- (=0), the notification should not be forwarded.
+ F bit
+ Forward bit. If set (=1), the notification should be forwarded
+ to the LSR for the next-hop or previous-hop for the LSP, if any,
+ associated with the event being signaled. If clear (=0), the
+ notification should not be forwarded.
Status Data
30-bit unsigned integer which specifies the status information.
This specification defines Status Codes (32-bit unsigned integers
with the above encoding).
A Status Code of 0 signals success.
Message ID
If non-zero, 32-bit value that identifies the peer message to which
the Status TLV refers. If zero, no specific peer message is being
identified.
Message Type
If non-zero, the type of the peer message to which the Status TLV
refers. If zero, the Status TLV does not refer to any specific
peer message.
-3.4. LDP Messages
+3.5. LDP Messages
- All LDP messages have the following TLV format:
+ All LDP messages have the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Message Type | Message Length |
+ |U| Message Type | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Mandatory Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Optional Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ U bit
+ Unknown message bit. Upon receipt of an unknown message, if U is
+ clear (=0), a notification is returned to the message originator;
+ if U is set (=1), the unknown message is silently ignored.
+
Message Type
Identifies the type of message
Message Length
- Specifies the length of the message value component (Mandatory plus
- Optional Parameters) in octets
+ Specifies the cumulative length in octets of the Message ID, Manda-
+ tory Parameters, and Optional Parameters.
Message Id
- Four octet integer used to identify this message. Used by the
- sending LSR to facilitate identifying notification messages that
- may apply to this message. An LSR sending a notification message
- in response to this message will include this Message Id in the
- notification message; see Section "Notification Message".
+ 32-bit value used to identify this message. Used by the sending
+ LSR to facilitate identifying notification messages that may apply
+ to this message. An LSR sending a notification message in response
+ to this message should include this Message Id in the notification
+ message; see Section "Notification Message".
Mandatory Parameters
Variable length set of required message parameters. Some messages
have no required parameters.
For messages that have required parameters, the required parameters
MUST appear in the order specified by the individual message
specifications in the sections that follow.
Optional Parameters
Variable length set of optional message parameters. Many messages
have no optional parameters.
For messages that have optional parameters, the optional parameters
may appear in any order.
+ Note that there is no alignment requirement for the first octet of an
+ LDP message.
+
The following message types are defined in this version of LDP:
- Message Name Type Section Title
+ Message Name Section Title
+
+ Notification "Notification Message"
+ Hello "Hello Message"
+ Initialization "Initialization Message"
+ KeepAlive "KeepAlive Message"
+ Address "Address Message"
+ Address Withdraw "Address Withdraw Message"
+ Label Mapping "Label Mapping Message"
+ Label Request "Label Request Message"
+ Label Withdraw "Label Withdraw Message"
+ Label Release "Label Release Message"
- Notification 0x0001 "Notification Message"
- Hello 0x0100 "Hello Message"
- Initialization 0x0200 "Initialization Message"
- KeepAlive 0x0201 "KeepAlive Message"
- Address 0x0300 "Address Message"
- Address Withdraw 0x0301 "Address Withdraw Message"
- Label Mapping 0x0401 "Label Mapping Message"
- Label Request 0x0402 "Label Request Message"
- Label Withdraw 0x0403 "Label Withdraw Message"
- Label Release 0x0404 "Label Release Message"
- Label Query 0x0405 "Label Query Message"
- Explicit Route Request 0x0500 "Explicit Route Request Message"
- Explicit Route Response 0x0501 "Explicit Route Response Message"
The sections that follow specify the encodings and procedures for
these messages.
- Some of the above message are related to one another, for example the
- Label Mapping, Label Request, Label Withdraw, and Label Release mes-
- sages.
+ Some of the above messages are related to one another, for example
+ the Label Mapping, Label Request, Label Withdraw, and Label Release
+ messages.
While is possible to think about messages related in this way in
terms of a message type that specifies a message class and a message
subtype that specifies a particular kind of message within that
class, this specification does not formalize the notion of a message
subtype.
The specification assigns type values for related messages, such as
the label messages, from of a contiguous block in the 16-bit message
type number space.
-3.4.1. Notification Message
+3.5.1. Notification Message
An LSR sends a Notification message to inform an LDP peer of a signi-
ficant event. A Notification message signals a fatal error or pro-
- vides advisory information regarding an item such as the processing
- of LDP messages or the state of the LDP session.
+ vides advisory information such as the outcome of processing an LDP
+ message or the state of the LDP session.
The encoding for the Notification Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Notification (0x0001) | Message Length |
+ |U| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
Status TLV
- Indicates the event being signalled. The encoding for the Status
+ Indicates the event being signaled. The encoding for the Status
TLV is specified in Section "Status TLV".
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV. The following Optional Parameters are generic
and may appear in any Notification Message:
Optional Parameter Type Length Value
Extended Status 0x0301 4 See below
+ Returned PDU 0x0302 var See below
+ Returned Message 0x0303 var See below
Other Optional Parameters, specific to the particular event being
- signalled by the Notification Messages may appear. These are
+ signaled by the Notification Messages may appear. These are
described elsewhere.
Extended Status
The 4 octet value is an Extended Status Code that encodes addi-
tional information that supplements the status information con-
tained in the Notification Status Code.
-3.4.1.1. Notification Message Procedures
+ Returned PDU
+ An LSR uses this parameter to return part of an LDP PDU to the
+ LSR that sent it. The value of this TLV is the PDU header and
+ as much PDU data following the header as appropriate for the
+ condition being signalled by the Notification message.
+
+ Returned Message
+ An LSR uses this parameter to return part of an LDP message to
+ the LSR that sent it. The value of this TLV is the message
+ type and length fields and as much message data following the
+ type and length fields as appropriate for the condition being
+ signalled by the Notification message.
+
+3.5.1.1. Notification Message Procedures
If an LSR encounters a condition requiring it to notify its peer with
advisory or error information it sends the peer a Notification mes-
sage containing a Status TLV that encodes the information and option-
ally additional TLVs that provide more information about the event.
If the condition is one that is a fatal error the Status Code carried
in the notification will indicate that. In this case, after sending
the Notification message the LSR should terminate the LDP session by
closing the session TCP connection and discard all state associated
with the session, including all label-FEC bindings learned via the
session.
When an LSR receives a Notification message that carries a Status
Code that indicates a fatal error, it should terminate the LDP ses-
sion immediately by closing the session TCP connection and discard
all state associated with the session, including all label-FEC bind-
ings learned via the session.
-3.4.1.2. Events Signalled by Notification Messages
+3.5.1.2. Events Signaled by Notification Messages
- It is useful for descriptive purpose to classify events signalled by
+ It is useful for descriptive purpose to classify events signaled by
Notification Messages into the following categories.
-3.4.1.2.1. Malformed PDU or Message
+3.5.1.2.1. Malformed PDU or Message
Malformed LDP PDUs or Messages that are part of the LDP Discovery
mechanism are handled by silently discarding them.
An LDP PDU received on a TCP connection for an LDP session is mal-
formed if:
- The LDP Identifier in the PDU header is unknown to the receiver,
or it is known but is not the LDP Identifier associated by the
- receiver with the LDP session. This is a fatal error signalled
- by the Bad LDP Identifier Status Code.
+ receiver with the LDP session. This is a fatal error signaled by
+ the Bad LDP Identifier Status Code.
- The LDP protocol version is not supported by the receiver, or it
is supported but is not the version negotiated for the session
- during session establishment. This is a fatal error signalled by
+ during session establishment. This is a fatal error signaled by
the Bad Protocol Version Status Code.
- - The PDU Length field is too short (< 20) or too long (> TBD).
- This is a fatal error signaled by the Bad PDU Length Status Code.
+ - The PDU Length field is too short (< 20) or too long
+ (> maximum PDU length). This is a fatal error signaled by the
+ Bad PDU Length Status Code. Section "Initialization Message"
+ describes how the maximum PDU length for a session is determined.
An LDP Message is malformed if:
- - The Message Type is unknown. See Section "Unknown Message Types"
- for more detail.
+ - The Message Type is unknown.
- If the Message Type is < 0x80000000 (high order bit = 0) it is a
- fatal error signalled by the Unknown Message Type Status Code.
+ If the Message Type is < 0x8000 (high order bit = 0) it is a
+ fatal error signaled by the Unknown Message Type Status Code.
- If the Message Type is >= 0x8000000 (high order bit = 1) it is
+ If the Message Type is >= 0x8000 (high order bit = 1) it is
silently discarded.
- The Message Length is too large, that is, indicates that the mes-
sage extends beyond the end of the containing LDP PDU. This is a
- fatal error signalled by the Bad Message Length Status Code.
+ fatal error signaled by the Bad Message Length Status Code.
-3.4.1.2.2. Unknown or Malformed TLV
+3.5.1.2.2. Unknown or Malformed TLV
Malformed TLVs contained in LDP messages that are part of the LDP
Discovery mechanism are handled by silently discarding the containing
message.
A TLV contained in an LDP message received on a TCP connection of an
LDP is malformed if:
- The TLV Length is too large, that is, indicates that the TLV
extends beyond the end of the containing message. This is a
- fatal error signalled by the Bad TLV Length Status Code.
+ fatal error signaled by the Bad TLV Length Status Code.
- - The TLV type is unknown. See Section "Unknown TLV in Known Mes-
- sage Type" for more detail.
+ - The TLV type is unknown.
- If the TLV type is < 0x80000000 (high order bit 0) it is a fatal
- error signalled by the Unknown TLV Status Code.
+ If the TLV type is < 0x8000 (high order bit 0) it is a fatal
+ error signaled by the Unknown TLV Status Code.
- If the TLV type is >= 0800000000 (high order bit 1) the TLV is
+ If the TLV type is >= 08000 (high order bit 1) the TLV is
silently dropped. Section "Unknown TLV in Known Message Type"
elaborates on this behavior.
- The TLV Value is malformed. This occurs when the receiver han-
- dles the TLV but cannot decode the TLV Value. This is
- intrepreted as indicative of a bug in either the sending or
- receiving LSR. It is a fatal error signalled by the Malformed
- TLV Value Status Code.
+ dles the TLV but cannot decode the TLV Value. This is inter-
+ preted as indicative of a bug in either the sending or receiving
+ LSR. It is a fatal error signaled by the Malformed TLV Value
+ Status Code.
-3.4.1.2.3. Session Hold Timer Expiration
+3.5.1.2.3. Session Hold Timer Expiration
- This is a fatal error signalled by the Hold Timer Expired Status
- Code.
+ This is a fatal error signaled by the Hold Timer Expired Status Code.
-3.4.1.2.4. Unilateral Session Shutdown
+3.5.1.2.4. Unilateral Session Shutdown
- This is a non-fatal event signalled by the Shutdown Status Code. The
+ This is a fatal event signaled by the Shutdown Status Code. The
Notification Message may optionally include an Extended Status TLV to
- provide a reason for the Shutdown. Note that although this is a
- "non-fatal" event, the sending LSR terminates the session immediately
- after sending the Notification.
+ provide a reason for the Shutdown. The sending LSR terminates the
+ session immediately after sending the Notification.
-3.4.1.2.5. Initialization Message Events
+3.5.1.2.5. Initialization Message Events
The session initialization negotiation (see Section "Session Initial-
ization") may fail if the session parameters received in the Initial-
ization Message are unacceptable. This is a fatal error. The
specific Status Code depends on the parameter deemed unacceptable,
- and are defined in Sections "Initialization Message Notification
- Status Codes".
+ and is defined in Sections "Initialization Message".
-3.4.1.2.6. Events Resulting From Other Messages
+3.5.1.2.6. Events Resulting From Other Messages
Messages other than the Initialization message may result in events
- that must be signalled to LDP peers via Notification Messages. These
+ that must be signaled to LDP peers via Notification Messages. These
events and the Status Codes used in the Notification Messages to sig-
nal them are described in the sections that describe these messages.
-3.4.1.2.7. Explicitly Routed LSP Setup Events
-
- Establishment of an Explicitly Routed LSP may fail for a variety of
- reasons. All such failures are considered non-fatal conditions and
- they are signalled by the Explicit Response Message.
-
-3.4.1.2.8. Miscellaneous Events
+3.5.1.2.7. Miscellaneous Events
These are events that fall into none of the categories above. There
are no miscellaneous events defined in this version of the protocol.
-3.4.2. Hello Message
+3.5.2. Hello Message
LDP Hello Messages are exchanged as part of the LDP Discovery Mechan-
ism; see Section "LDP Discovery".
The encoding for the Hello Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Hello (0x0100) | Message Length |
+ |U| Hello (0x0100) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Common Hello Parameters TLV |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
+
+ Common Hello Parameters TLV
+ Specifies parameters common to all Hello messages. The encoding
+ for the Common Hello Parameters TLV is:
+
+ 0 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |U|F| Common Hello Parms(0x0400)| Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Hold Time |T|R| Reserved |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Hold Time,
+ Hello hold time in seconds. An LSR maintains a record of Hellos
+ received from potential peers (see Section "Hello Message Pro-
+ cedures"). Hello Hold Time specifies the time the sending LSR
+ will maintain its record of Hellos from the receiving LSR without
+ receipt of another Hello.
+
+ A pair of LSRs negotiates the hold times they use for Hellos from
+ each other. Each proposes a hold time. The hold time used is
+ the minimum of the hold times proposed in their Hellos.
+
+ A value of 0 means use the default. There are interface type
+ specific defaults for Link Hellos as well as a default for Tar-
+ geted Hellos. A value of 0xfffff means infinite.
+
+ T, Targeted Hello
+ A value of 1 specifies that this Hello is a Targeted Hello. A
+ value of 0 specifies that this Hello is a Link Hello.
+
+ R, Request Send Targeted Hellos
+ A value of 1 requests the receiver to send periodic Targeted Hel-
+ los to the source of this Hello. A value of 0 makes no request.
+
+ An LSR initiating Extended Discovery sets R to 1. If R is 1, the
+ receiving LSR checks whether it has been configured to send Tar-
+ geted Hellos to the Hello source in response to Hellos with this
+ request. If not, it ignores the request. If so, it initiates
+ periodic transmission of Targeted Hellos to the Hello source.
+
+ Reserved
+ This field is reserved. It must be set to zero on transmission
+ and ignored on receipt.
Optional Parameters
This variable length field contains 0 or more parameters, each
- encoded as a TLV. The optional parameters defined by this version
- of the protocol are
- Optional Parameter Type Length Value
-
- Targeted Hello 0x0400 0 --
- Send Targeted Hello 0x0401 0 --
- Transport Address 0x0402 4 See below
- Hello Hold Time 0x0403 4 See below
+ encoded as a TLV. The optional parameters defined by this ver-
+ sion of the protocol are
- Targeted Hello
- This Hello is a Targeted Hello. Without this optional parameter
- the Hello is a Link Hello.
+ Optional Parameter Type Length Value
- Send Targeted Hello
- Requests the receiver to send periodic Targeted Hellos to the
- source of this Hello. An LSR initiating Extended Discovery uses
- this option.
+ Transport Address 0x0401 4 See below
+ Configuration 0x0402 4 See below
+ Sequence Number
Transport Address
Specifies the IPv4 address to be used for the sending LSR when
- opening the LDP session TCP connection. If this optional TLV is
- not present the IPv4 source address for the UDP packet carrying
- the Hello should be used.
+ opening the LDP session TCP connection. If this optional TLV
+ is not present the IPv4 source address for the UDP packet car-
+ rying the Hello should be used.
- Hello Hold Time
- An LSR maintains a record of Hellos received from potential peers
- (see below) When present, this parameter specifies the time in
- seconds the sending LSR will maintain its record of Hellos from
- the receiving LSR without receipt of another Hello. When not
- present, the sender will use a default hold time. There are
- interface type specific defaults for Link Hellos as well a
- default for Targeted Hellos.
+ Configuration Sequence Number
+ Specifies a 4 octet unsigned configuration sequence number that
+ identifies the configuration state of the sending LSR. Used by
+ the receiving LSR to detect configuration changes on the
+ sending LSR.
-3.4.2.1. Hello Message Procedures
+3.5.2.1. Hello Message Procedures
An LSR receiving Hellos from another LSR maintains a Hello adjacency
- for the Hellos. The LSR maintains a hold timer with the Hello adja-
- cency which it restarts whenever it receives a Hello that matches the
- Hello adjacency. If the hold timer for a Hello adjacency expires the
- LSR discards the Hello adjacency: see sections "Maintaining Hello
- Adjacencies" and "Maintaining LDP Sessions".
+ corresponding to the Hellos. The LSR maintains a hold timer with the
+ Hello adjacency which it restarts whenever it receives a Hello that
+ matches the Hello adjacency. If the hold timer for a Hello adjacency
+ expires the LSR discards the Hello adjacency: see sections "Maintain-
+ ing Hello Adjacencies" and "Maintaining LDP Sessions".
- A LSR processes a received LDP Hello as follows:
+ We recommend that the interval between Hello transmissions be at most
+ one third of the Hello hold time.
+
+ An LSR processes a received LDP Hello as follows:
1. The LSR checks whether the Hello is acceptable. The criteria
for determining whether a Hello is acceptable are implementa-
tion dependent (see below for example criteria).
2. If the Hello is not acceptable, the LSR ignores it.
3. If the Hello is acceptable, the LSR checks whether it has a
Hello adjacency for the Hello source. If so, it restarts the
hold timer for the Hello adjacency. If not it creates a Hello
adjacency for the Hello source and starts its hold timer.
4. If the Hello carries any optional TLVs the LSR processes them
(see below).
5. Finally, if the LSR has no LDP session for the label space
- specified by the LDP identifier in the common header for the
- Hello, it attempts to establish a session for the label space;
- see section "LDP Session Establishment".
+ specified by the LDP identifier in the PDU header for the
+ Hello, it follows the procedures of Section "LDP Session Estab-
+ lishment".
The following are examples of acceptability criteria for Link and
Targeted Hellos:
A Link Hello is acceptable if the interface on which it was
received has been configured for label switching.
A Targeted Hello from IP source address a.b.c.d is acceptable if
either:
- The LSR has been configured to accept Targeted Hellos, or
- The LSR has been configured to send Targeted Hellos to
a.b.c.d.
The following describes how an LSR processes Hello optional TLVs:
- Targeted Hello
- No special processing required.
-
- Send Targeted Hello
- If the Send Targeted Hello option is carried by the Hello,
- the LSR checks whether it has been configured to send Tar-
- geted Hellos to the Hello source in response to Hellos with
- this option. If not, it ignores the option. If so, it
- initiates periodic transmission of Targeted Hellos to the
- Hello source.
-
Transport Address
The LSR associates the specified transport address with the
Hello adjacency.
- Hello Hold Time
- A pair of LSRs negotiate the hold times they use for Hellos
- from each other. Each LSR proposes a hold time in its Hel-
- los either explicitly by including the Hold Time optional
- TLV or implicitly by omitting it. The hold time used by
- the LSRs is the minimum of the hold times proposed in their
- Hellos.
+ Configuration Sequence Number
+ The Configuration Sequence Number optional parameter is used by
+ the sending LSR to signal configuration changes to the receiv-
+ ing LSR. When a receiving LSR playing the active role in LDP
+ session establishment detects a change in the sending LSR con-
+ figuration, it may clear the session setup backoff delay, if
+ any, associated with the sending LSR (see Section "Session Ini-
+ tialization").
- We recommend that the interval between Hello transmissions be at
- most one third of the Hello hold time.
+ A sending LSR using this optional parameter is responsible for
+ maintaining the configuration sequence number it transmits in
+ Hello messages. Whenever there is a configuration change on
+ the sending LSR, it increments the configuration sequence
+ number.
-3.4.3. Initialization Message
+3.5.3. Initialization Message
The LDP Initialization Message is exchanged as part of the LDP ses-
sion establishment procedure; see Section "LDP Session Establish-
ment".
The encoding for the Initialization Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Initialization (0x0200) | Message Length |
+ |U| Initialization (0x0200) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Session Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
Common Session Parameters TLV
Specifies values proposed by the sending LSR for parameters common
to all LDP sessions.
- The encoding for the Basic Session Parameters TLV is:
+ The encoding for the Common Session Parameters TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Common Sess Params (0x0500) | Message Length |
+ |U|F| Common Sess Parms (0x0500)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Version | Hold Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |A|D| PVLim | Reserved | Max PDU Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver LDP Identifer |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
Protocol Version
Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP pro-
tocol version 1.
Hold Time
Two octet unsigned non zero integer that indicates the number
of seconds that the sending LSR proposes for the value of the
KeepAlive Interval. The receiving LSR MUST calculate the value
of the KeepAlive Timer by using the smaller of its proposed
Hold Time and the Hold Time received in the PDU. The value
chosen for Hold Time indicates the maximum number of seconds
that may elapse between the receipt of successive PDUs from the
- LSR peer. The Keepalive Timer is reset each time a PDU
+ LDP peer. The KeepAlive Timer is reset each time a PDU
arrives.
+ A, Label Advertisement Discipline
+ Indicates the type of Label advertisement. A value of 0 means
+ Downstream Unsolicited advertisement; a value of 1 means Down-
+ stream On Demand.
+
+ If one LSR proposes Downstream Unsolicted and the other pro-
+ poses Downstream on Demand, the rules for resolving this
+ difference is:
+
+ - If the session is for a label-controlled ATM link or a
+ label-controlled Frame Relay link, then Downstream on
+ Demand must be used.
+
+ - Otherwise, Downstream Unsolicted must be used.
+
+ If the label advertisement discipline determined in this way is
+ unacceptable to an LSR, it must send a Session
+ Rejected/Parameters Advertisement Mode Notification message in
+ response to the Initialization message and not establish the
+ session.
+
+ D, Loop Detection
+ Indicates whether loop detection based on path vectors is
+ enabled. A value of 0 means loop detection is disabled; a
+ value of 1 means that loop detection is enabled.
+
+ PVLim, Path Vector Limit
+ The configured maximum path vector length. Must be 0 if loop
+ detection is disabled (D = 0). If the loop detection pro-
+ cedures would require the LSR to send a path vector that
+ exceeds this limit, the LSR will behave as if a loop had been
+ detected for the FEC in question.
+
+ When Loop Detection is enabled in a portion of a network, it is
+ recommended that all LSRs in that portion of the network be
+ configured with the same path vector limit. Although
+ knowledege of a peer's path vector limit will not change an
+ LSR's behavior, it does enable the LSR to alert an operator to
+ a possible misconfiguration.
+
+ Reserved
+ This field is reserved. It must be set to zero on transmission
+ and ignored on receipt.
+
+ Max PDU Length
+ Two octet unsigned integer that proposes the maximum allowable
+ length for LDP PDUs for the session. A value of 255 or less
+ specifies the default maximum length of 4096 octets.
+
+ The receiving LSR MUST calculate the maximum PDU length for the
+ session by using the smaller of its and its peer's proposals
+ for Max PDU Length. The default maximum PDU length applies
+ before session initialization completes.
+
+ If the maximum PDU length determined this way is unacceptable
+ to an LSR, it must send a Session Rejected/Parameters Max PDU
+ Length Notification message in response to the Initialization
+ message and not establish the session.
+
Receiver LDP Identifer
Identifies the receiver's label space. This LDP Identifier,
- together with the sender's LDP Identifier in the common header
+ together with the sender's LDP Identifier in the PDU header
enables the receiver to match the Initialization message with
one of its Hello adjacencies; see Section "Hello Message Pro-
cedures".
+ If there is no matching Hello adjacency, the LSR must send a
+ Session Rejected/No Hello Notification message in response to
+ the Initialization message and not establish the session.
+
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are:
Optional Parameter Type Length Value
- Label Allocation 0x0501 1 See below
- Discipline
- Loop Detection 0x0502 0 --
- Merge 0x0503 1 See below
- ATM Null Encapsulation 0x0504 0 --
- ATM Label Range 0x0600 8 See below
- Frame Relay Label Range 0x0601 8 See below
+ ATM Session Parameters 0x0501 var See below
+ Frame Relay Session 0x0502 var See below
+ Parameters
- Label Allocation Discipline
- Indicates the type of Label allocation. A value of 0 is
- Downstream allocation, A value of 1 is Downstream On Demand.
- If this optional parameter is not specfied, Downstream alloca-
- tion is used.
+ ATM Session Parameters
+ Used when an LDP session manages label exchange for an ATM link
+ to specify ATM-specific session parameters.
- Loop Detection
- If present, indicates that Loop Detection is enabled. If
- absent, Loop Detection is disabled.
+ 0 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |U|F| ATM Sess Parms (0x0501) | Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | M | N |E| Reserved |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | ATM Label Range Component 1 |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ ~ ~
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | ATM Label Range Component N |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Merge
- Specifies the merge capabilities of an ATM or Frame Relay
- switch. The following values are supported in this version of
- the specification:
+ M, ATM Merge Capabilities
+ Specifies the merge capabilities of an ATM switch. The follow-
+ ing values are supported in this version of the specification:
Value Meaning
0 Merge not supported
-
- For ATM Merge:
1 VP Merge supported
2 VC Merge supported
3 VP & VC Merge supported
- For Frame Relay Merge:
- Non-zero Merge supported
+ If the merge capabilities of the LSRs differ, then:
- ATM Null Encapsulation
- If present, specifies that the LSR supports the null
+ - Non-merge and VC-merge LSRs may freely interoperate.
+
+ - The interoperability of VP-merge-capable switches with
+ non-VPN-merge-capable switches is a subject for future
+ study.
+
+ Note that if VP merge is used, it is the responsibility of the
+ ingress node to ensure that the chosen VCI is unique within the
+ LSR domain.
+
+ N, Number of label range components
+ Specifies the number of ATM Label Range Components included in
+ the TLV.
+
+ E, ATM Null Encapsulation
+ A value of 1 specifies specifies that the LSR supports the null
encapsulation of [rfc1483] for its data VCs on the ATM link
- managed by the LDP session. In this case IP packets are
- carried directly inside AAL5 frames. If absent, the null
- encapsulation is not supported.
+ managed by the LDP session. In this case IP packets are car-
+ ried directly inside AAL5 frames. A value of 0 specifies that
+ the null encapsulation is not supported.
- ATM Label Range
- Used when an LDP session manages label exchange for an ATM link.
- The ATM Label Range TLV contains the label range supported by the
- transmitting LSR. A receiving LSR MUST calculate the intersection
- between the received range and its own supported label range. The
- intersection is the range in which the LSR may allocate and accept
- labels. LSRs may NOT establish an adjacency with neighbors whose
- intersection range is NULL.
+ Reserved
+ This field is reserved. It must be set to zero on transmission
+ and ignored on receipt.
+
+ One or more ATM Label Range Components
+ A list of ATM Label Range Components which together specify the
+ Label range supported by the transmitting LSR.
+
+ A receiving LSR MUST calculate the intersection between the
+ received range and its own supported label range. The inter-
+ section is the range in which the LSR may allocate and accept
+ labels. LSRs MUST NOT establish a session with neighbors for
+ which the intersection of ranges is NULL. In this case, the
+ LSR must send a Session Rejected/Parameters Label Range Notifi-
+ cation message in response to the Initialization message and
+ not establish the session.
+
+ The encoding for an ATM Label Range Component is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Minimum VPI | Minimum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Maximum VPI | Maximum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res
@@ -2603,1104 +2485,2589 @@
justified in this field and preceding bits should be set to
0.
Maximum VCI (16 bits)
This 16 bit field specifies the upper bound of a block of
Virtual Connection Identifiers that is supported on the ori-
ginating switch. If the VCI is less than 16-bits it should
be right justified in this field and preceding bits should be
set to 0.
- Frame Relay Label Range
- Used when an LDP session manages label exchange for a Frame
- Relay link. The Frame Relay Label Range TLV contains the label
- range supported by the transmitting LSR. A receiving LSR MUST
- calculate the intersection between the received range and its
- own supported label range. The intersection is the range in
- which the LSR may allocate and accept labels. LSRs may NOT
- establish an adjacency with neighbors whose intersection range
- is NULL.
+ Frame Relay Session Parameters
+ Used when an LDP session manages label exchange for a Frame Relay
+ link to specify Frame Relay-specific session parameters.
+
+ 0 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |U|F| FR Sess Parms (0x0502) | Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | M | N | Reserved |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Frame Relay Label Range Component 1 |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ ~ ~
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Frame Relay Label Range Component N |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ M, Frame Relay Merge Capabilities
+ Specifies the merge capabilities of a Frame Relay switch. The
+ following values are supported in this version of the specifi-
+ cation:
+
+ Value Meaning
+
+ 0 Merge not supported
+ 1 Merge supported
+
+ Non-merge and merge Frame Relay LSRs may freely interoperate.
+
+ N, Number of label range components
+ Specifies the number of Frame Relay Label Range Components
+ included in the TLV.
+
+ Reserved
+ This field is reserved. It must be set to zero on transmission
+ and ignored on receipt.
+
+ One or more Frame Relay Label Range Components
+ A list of Frame Relay Label Range Components which together
+ specify the Label range supported by the transmitting LSR.
+
+ A receiving LSR MUST calculate the intersection between the
+ received range and its own supported label range. The inter-
+ section is the range in which the LSR may allocate and accept
+ labels. LSRs MUST NOT establish a session with neighbors for
+ which the intersection of ranges is NULL. In this case, the
+ LSR must send a Session Rejected/Parameters Label Range Notifi-
+ cation message in response to the Initialization message and
+ not establish the session.
+
+ The encoding for a Frame Relay Label Range Component is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| Minimum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Maximum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Reserved
+ This field is reserved. It must be set to zero on transmis-
+ sion and ignored on receipt.
+
Len
This field specifies the number of bits of the DLCI. The
following values are supported:
Len DLCI bits
0 10
1 17
2 23
-3.4.3.1. Initialization Message Procedures
+ Minimum DLCI
+ This 23-bit vield specifies the lower bound of a block of
+ Data Link Connection Identifiers (DLCIs) that is supported on
+ the originating switch. The DLCI should be right justified
+ in this field and unused bits should be set to 0.
+
+ Maximum DLCI
+ This 23-bit vield specifies the upper bound of a block of
+ Data Link Connection Identifiers (DLCIs) that is supported on
+ the originating switch. The DLCI should be right justified
+ in this field and unused bits should be set to 0.
+
+ Note that there is no Generic Session Parameters TLV for sessions
+ which advertise Generic Labels.
+
+3.5.3.1. Initialization Message Procedures
See Section "LDP Session Establishment" and particularly Section
- "Session Initialization" for general procedures for handling the Ini-
- tialization Message.
+ "Session Initialization" for general procedures for handling the
+ Initialization Message.
-3.4.4. KeepAlive Message
+3.5.4. KeepAlive Message
An LSR sends KeepAlive Messages as part of a mechanism that monitors
the integrity of the LDP session transport connection.
The encoding for the KeepAlive Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | KeepAlive (0x0201) | Message Length |
+ |U| KeepAlive (0x0201) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
Optional Parameters
No optional parameters are defined for the KeepAlive message.
-3.4.4.1. KeepAlive Message Procedures
+3.5.4.1. KeepAlive Message Procedures
The Hold Timer mechanism described in Section "Maintaining LDP Ses-
- sions" resets a seesion hold timer every time an LDP PDU is received.
+ sions" resets a session hold timer every time an LDP PDU is received.
The KeepAlive Message is provided to allow reset of the Hold Timer in
circumstances where an LSR has no other information to communicate to
an LDP peer.
- An LSR must arrange that its peer sees an LDP Message from it at
- least every Hold Time period. That message may be any other from the
- protocol or, in circumstances where there is no need to send one of
- them, it must be KeepAlive Message.
+ An LSR must arrange that its peer receive an LDP Message from it at
+ least every Hold Time period. Any LDP protocol message will do but,
+ in circumstances where no other LDP protocol messages have been sent
+ within the period, a KeepAlive message must be sent.
-3.4.5. Address Message
+3.5.5. Address Message
An LSR sends the Address Message to an LDP peer to advertise its
interface addresses.
The encoding for the Address Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Address (0x0300) | Message Length |
+ |U| Address (0x0300) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address List TLV |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
Address List TLV
The list of interface addresses being advertised by the sending
LSR. The encoding for the Address List TLV is specified in Section
"Address List TLV".
Optional Parameters
No optional parameters are defined for the Address message.
-3.4.5.1. Address Message Procedures
+3.5.5.1. Address Message Procedures
An LSR that receives an Address Message message uses the addresses it
learns to maintain a database for mapping between peer LDP Identif-
- iers and next hop addresses; see section "LDP Identifiers and Next
+ iers and next hop addresses; see Section "LDP Identifiers and Next
Hop Addresses".
When a new LDP session is initialized and before sending Label Map-
- ping or Label Request messages and LSR should advertise its interface
+ ping or Label Request messages an LSR should advertise its interface
addresses with one or more Address messages.
Whenever an LSR "activates" a new interface address, it should adver-
tise the new address with an Address message.
Whenever an LSR "de-activates" a previously advertised address, it
should withdraw the address with an Address Withdraw message; see
Section "Address Withdraw Message".
-3.4.6. Address Withdraw Message
+3.5.6. Address Withdraw Message
An LSR sends the Address Message to an LDP peer to withdraw previ-
ously advertised interface addresses.
The encoding for the Address Withdraw Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Address Withdraw (0x0301) | Message Length |
+ |U Address Withdraw (0x0301) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address List TLV |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
Address list TLV
The list of interface addresses being withdrawn by the sending LSR.
The encoding for the Address list TLV is specified in Section
"Address List TLV".
Optional Parameters
No optional parameters are defined for the Address Withdraw mes-
sage.
-3.4.6.1. Address Withdraw Message Procedures
+3.5.6.1. Address Withdraw Message Procedures
See Section "Address Message Procedures"
-3.4.7. Label Mapping Message
+3.5.7. Label Mapping Message
An LSR sends a Label Mapping message to an LDP peer to advertise
FEC-label bindings to the peer.
The encoding for the Label Mapping Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label Mapping (0x0400) | Message Length |
+ |U| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Label Mapping TLV 1 |
+ | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | |
- ~ ~
- | |
+ | Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Label Mapping TLV n |
+ | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
- FEC-Label Mapping TLV
- Each specifies a binding between an FEC and a label. A FEC-Label
- Mapping TLV is a nested TLV that contains a FEC TLV, a Label TLV,
- an optional COS TLF, an optional Hop Count TLV, and an optional
- Path Vector TLV:
+ FEC TLV
+ Specifies the FEC component of the FEC-Label mapping being adver-
+ tised. See Section "FEC TLV" for encoding.
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-label Mapping (0x0700) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | COS TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Hop Count TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Path Vector TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Label TLV
+ Specifies the Label component of the FEC-Label mapping. See Sec-
+ tion "Label TLV" for encoding.
- The encodings for the FEC, Label, COS, Hop Count, and Path Vector
- TLVs can be found in Section "Commonly Used TLVs".
+ Optional Parameters
+ This variable length field contains 0 or more parameters, each
+ encoded as a TLV. The optional parameters are:
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ Optional Parameter Length Value
- Need to add multipath possibility to above by allowing multiple
- label TLVs to the FEC-label Mapping TLV. This will be done with
- the addition:
+ Label Request 4 See below
+ Message Id
+ COS TLV 1 See below
+ Hop Count TLV 1 See below
+ Path Vector TLV variable See below
- Label TLV2 (optional)
- ...
- Label TLVn (optional)
+ The encodings for the COS, Hop Count, and Path Vector TLVs can be
+ found in Section "TLV Encodings for Commonly Used Parameters".
- with discussion.
+ Label Request Message Id
+ If this Label Mapping message is a response to a Label Request
+ message that carried the Return Message Id optional parameter
+ (see Section "Label Request Message") the Label Mapping message
+ must include the Request Message Id optional parameter. The
+ value of this optional parameter is the Message Id of the
+ corresponding Label Request Message.
- END NOTE * END NOTE * END NOTE:
+ COS
+ Specifies the Class of Service (COS) to be associated with the
+ FEC-Label mapping. If not present, the LSR should use its
+ default COS for IP packets as the COS.
- Optional Parameters
- No optional parameters are defined for the Label Mapping message.
+ Hop Count
+ Specifies the running total of the number of LSR hops along the
+ LSP being setup by the Label Message. Section "Hop Count Pro-
+ cedures" describes how to handle this TLV.
-3.4.7.1. Label Mapping Message Procedures
+ Path Vector
+ Specifies the LSRs along the LSP being setup by the Label Mes-
+ sage. Section "Path Vector Procedures" describes how to handle
+ this TLV.
+
+3.5.7.1. Label Mapping Message Procedures
The Mapping message is used by an LSR to distribute a label mapping
- for a FEC to its LDP peers. If an LSR distributes a mapping for a
- FEC to multiple LDP peers, it is a local matter whether it maps a
- single label to the FEC, and distributes that mapping to all its
- peers, or whether it uses a different mapping for each of its peers.
+ for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC
+ to multiple LDP peers, it is a local matter whether it maps a single
+ label to the FEC, and distributes that mapping to all its peers, or
+ whether it uses a different mapping for each of its peers.
- An LSR is always responsible for the consistency of the label map-
- pings it has distributed, and that its peers have these mappings.
+ An LSR is responsible for the consistency of the label map- pings it
+ has distributed, and that its peers have these mappings.
-3.4.7.1.1. Independent Control Mapping
+ See Appendx A "LDP Label Distribution Procedures" for more details.
+
+3.5.7.1.1. Independent Control Mapping
If an LSR is configured for independent control, a mapping message is
- transmitted by an LSR to peers upon any of the following conditions:
+ transmitted by the LSR upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and the
- label advertisement mode is Downstream allocation.
+ label advertisement mode is Downstream Unsolicited advertise-
+ ment.
- 2. The LSR receives a Request message from an upstream peer for an
+ 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table.
- 3. The next hop for an FEC changes to another LDP peer, and loop
+ 3. The next hop for a FEC changes to another LDP peer, and loop
detection is configured.
4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR
b) loop detection is configured OR
c) the attributes of the mapping have changed.
-3.4.7.1.2. Ordered Control Mapping
+3.5.7.1.2. Ordered Control Mapping
If an LSR is doing ordered control, a Mapping message is transmitted
by downstream LSRs upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and is
the egress for that FEC.
- 2. The LSR receives a Request message from an upstream peer for an
+ 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table, and the LSR is the
egress for that FEC OR has a downstream mapping for that FEC.
- 3. The next hop for an FEC changes to another LDP peer, and loop
+ 3. The next hop for a FEC changes to another LDP peer, and loop
detection is configured.
4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR
b) loop detection is configured OR
c) the attributes of the mapping have changed.
-3.4.7.1.3. Downstream-on-Demand Label Advertisement
+3.5.7.1.3. Downstream-on-Demand Label Advertisement
In general, the upstream LSR is responsible for requesting label map-
pings when operating in Downstream-on-Demand mode. However, unless
some rules are followed, it is possible for neighboring LSRs with
different advertisement modes to get into a livelock situation where
everything is functioning properly, but no labels are distributed.
For example, consider two LSRs Ru and Rd where Ru is the upstream LSR
and Rd is the downstream LSR for a particular FEC. In this example,
- Ru is using Downstream allocation mode and Rd is using Downstream-
- on-Demand mode. In this case, Rd may assume that Ru will request a
- label mapping when it wants one and Ru may assume that Rd will adver-
- tise a label if it wants Ru to use one. If Rd and Ru operate as sug-
- gested, no labels will be distributed and packets must be routed at
- layer-3.
+ Ru is using Downstream Unsolicited advertisement mode and Rd is using
+ Downstream-on-Demand mode. In this case, Rd may assume that Ru will
+ request a label mapping when it wants one and Ru may assume that Rd
+ will advertise a label if it wants Ru to use one. If Rd and Ru
+ operate as suggested, no labels will be distributed from Rd to Ru.
This livelock situation can be avoided if the following rule is
observed: an LSR operating in Downstream-on-Demand mode should not be
expected to send unsolicited mapping advertisements. Therefore, if
the downstream LSR is operating in Downstream-on-Demand mode, the
upstream LSR is responsible for requesting label mappings as needed.
- However, if all interfaces on an LSR are configured to operate in
- Downstream- on-Demand mode the LSR can wait to issue a request until
- a corresponding request has been sent from an upstream LSR.
-3.4.7.1.4. Downstream Allocation Label Advertisement
+3.5.7.1.4. Downstream Unsolicited Label Advertisement
In general, the downstream LSR is responsible for advertising a label
mapping when it wants an upstream LSR to use the label. An upstream
LSR may issue a mapping request if it so desires.
-3.4.8. Label Request Message
+3.5.8. Label Request Message
An LSR sends the Label Request Message to an LDP peer to request a
- binding (mapping) for one or more specific FECs.
+ binding (mapping) for a FEC.
The encoding for the Label Request Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label Request (0x0401) | Message Length |
+ |U| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Request TLV 1 |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | |
- ~ ~
- | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Request TLV n |
+ | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
+ 32-bit value used to identify this message.
- FEC-Request TLV
- Each specifies an FEC for which a label mapping is requested. A
- FEC-Request TLV is a nested TLV that contains a FEC TLV, an
- optional COS TLV, and an optional Hop Count TLV.
+ FEC TLV
+ The FEC for which a label is being requested. See Section "FEC
+ TLV" for encoding.
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Request (0x0701) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | COS TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Hop Count TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Optional Parameters
+ This variable length field contains 0 or more parameters, each
+ encoded as a TLV. The optional parameters are:
- The encodings for the FEC, COS, and Hop Count TLVs are specified in
- Section "Commonly Used TLVs".
+ Optional Parameter Length Value
- Optional Parameters
- No optional parameters are defined for the Label Request message.
+ Return Message Id 0 See below
+ COS TLV 1 See below
+ Hop Count TLV 1 See below
+ Path Vector TLV variable See below
-3.4.8.1. Label Request Message Procedures
+ The encodings for the COS, Hop Count, and Path Vector TLVs can be
+ found in Section "TLV Encodings for Commonly Used Parameters".
+
+ Return Message Id
+ Requests the LDP peer include the Message Id of this Label
+ Request message in its Label Mapping message response. If an
+ LDP peer receives a Label Request message with the Return Mes-
+ sage Id optional parameter, its Label Mapping message response
+ must contain a Label Request Message Id optional parameter with
+ the Message Id of the Label Request message. See Section
+ "Label Mapping Message".
+
+ COS
+ Specifies the Class of Service (COS) to be associated with the
+ requested FEC-Label mapping. If not present, the LSR should
+ use its default COS for IP packets as the COS.
+
+ Hop Count
+ Specifies the running total of the number of LSR hops along the
+ LSP being setup by the Label Request Message. Section "Hop
+ Count Procedures" describes how to handle this TLV.
+
+ Path Vector
+ Specifies the LSRs along the LSR being setup by the Label
+ Request Message. Section "Path Vector Procedures" describes
+ how to handle this TLV.
+
+3.5.8.1. Label Request Message Procedures
The Request message is used by an upstream LSR to explicitly request
- that the downstream LSR assign and advertise a label for an FEC.
+ that the downstream LSR assign and advertise a label for a FEC.
- An LSR transmits a Request message under any of the following condi-
- tions:
+ An LSR may transmit a Request message under any of the following con-
+ ditions:
1. The LSR recognizes a new FEC via the forwarding table, and the
- next hop is an Operational LDP peer, and the LSR doesn't
- already have a mapping from the next hop for the given FEC.
+ next hop is an LDP peer, and the LSR doesn't already have a
+ mapping from the next hop for the given FEC.
2. The next hop to the FEC changes, and the LSR doesn't already
have a mapping from that next hop for the given FEC.
- If a request cannot be satisfied by the downstream LSR, the request-
- ing LSR may optionally choose to request again at a later time, or,
- if the downstream LSR is configured for Downstream Allo- cation, the
- requesting LSR may wait for the mapping, assuming that the downstream
- LSR will provide the mapping automatically when it is available.
+ 3. The LSR receives a Label Request for a FEC from an upstream LDP
+ peer, the FEC next hop is an LDP peer, and the LSR doesn't
+ already have a mapping from the next hop.
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ The receiving LSR should respond to a Label Request message with a
+ Label Mapping for the requested label or with a Notification message
+ indicating why it cannot satisfy the request.
- In the case where the downstream LSR is doing DoD, how does the
- requesting LSR decide when to make its request?
+ This version of the protocol defines the following Status Codes for
+ the Notification message that signals a request cannot be satisfied:
- TDP addresses this issue by having a "now I have label resources"
- message which it sends to downwstream peers whose requests it has
- denied. This serves as a signal to them to re-issue their
- requests. LDP should probably have this. Without such a signal,
- the denied requester has no recourse but to periodically retry.
+ No Route
+ The FEC for which a label was requested is for a Prefix FEC Ele-
+ ment, and the LSR does not have a route for that prefix.
- END NOTE * END NOTE * END NOTE:
+ No Label Resources
+ The LSR cannot provide a label because of resource limitations.
+ When resources become available the LSR must notify the request-
+ ing LSR by sending a Notification message with the Label
+ Resources Available Status Code.
-3.4.9. Label Withdraw Message
+ An LSR that receives a No Label Resources response to a Label
+ Request message must not issue further Label Request messages
+ until it receives a Notification message with the Label Resources
+ Available Status code.
+
+ Loop Detected
+ The LSR has detected a looping Label Requst message.
+
+ See Appendx A "LDP Label Distribution Procedures" for more details.
+
+3.5.9. Label Withdraw Message
An LSR sends a Label Withdraw Message to an LDP peer to signal the
peer that the peer may not continue to use specific FEC-label map-
pings the LSR had previously advertised. This breaks the mapping
between the FECs and the labels.
The encoding for the Label Withdraw Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label Withdraw (0x0402) | Message Length |
+ |U| Label Withdraw (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Withdraw-Release TLV 1 |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | |
- ~ ~
- | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Withdraw-Release TLV n |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Optional Parameters |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
- Message Id
- Four octet integer used to identify this message.
-
- FEC-Withdraw-Release TLV
- Each TLV specifies a FEC-label mapping being withdrawn. A FEC-
- Withdraw-Release TLV is a nested TLV that contains a FEC TLV and an
- optional label TLV.
-
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Withdraw-Release (0x0702) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- The encodings for the FEC and Label TLVs are specified in Section
- "Commonly Used TLVs".
+ Message Id
+ 32-bit value used to identify this message.
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ FEC TLV
+ Identifies the FEC for which the FEC-label mapping is being with-
+ drawn.
- Need to add multipath possibility to above by allowing multiple
- label TLVs to the FEC-label Mapping TLV. This will be done with
- the addition:
+ Optional Parameters
+ This variable length field contains 0 or more parameters, each
+ encoded as a TLV. The optional parameters are:
- Label TLV2 (optional)
- ...
- Label TLVn (optional)
+ Optional Parameter Length Value
- with discussion.
+ Label TLV variable See below
- END NOTE * END NOTE * END NOTE:
+ The encoding for Label TLVs are found in Section "Label TLVs".
- Optional Parameters
- No optional parameters are defined for the Label Withdraw message.
+ Label
+ If present, specifies the label being withdrawn (see procedures
+ below).
-3.4.9.1. Label Withdraw Message Procedures
+3.5.9.1. Label Withdraw Message Procedures
- An LSR transmits a Withdraw message under the following condition:
+ An LSR transmits a Label Withdraw message under the following condi-
+ tions:
1. The LSR no longer recognizes a previously known FEC.
- 2. Optionally, the LSR has unspliced an upstream label from the
- downstream label.
+ 2. The LSR has decided unilaterally (e.g., via configuration) to
+ no longer label switch a FEC (or FECs) with the label mapping
+ being withdrawn.
- The FEC in the FEC-Withdraw-Release TLV is a FEC for which labels are
- to be withdrawn. If no label TLV follows the FEC, all labels associ-
- ated with the FEC are to be withdrawn, else only the labels specified
- in the following Label TLV are to be withdrawn.
+ The FEC TLV specifies the FEC for which labels are to be withdrawn.
+ If no Label TLV follows the FEC, all labels associated with the FEC
+ are to be withdrawn; otherwise only the label specified in the
+ optional Label TLV is to be withdrawn.
-3.4.10. Label Release Message
+ The FEC TLV may contain the Wildcard FEC Element; if so, it may con-
+ tain no other FEC Elements. In this case, if the Label Withdraw mes-
+ sage contains an optional Label TLV, then the label is to be with-
+ drawn from all FECs to which it is bound. If there is not an
+ optional Label TLV in the Label Withdraw message, then the sending
+ LSR is withdrawing all label mappings previously advertised to the
+ receiving LSR.
+
+ See Appendx A "LDP Label Distribution Procedures" for more details.
+
+3.5.10. Label Release Message
An LSR sends a Label Release message to an LDP peer to signal the
peer that the LSR no longer needs specific FEC-label mappings previ-
ously requested of and/or advertised by the peer.
The encoding for the Label Release Message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label Release (0x0403) | Message Length |
+ |U| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Withdraw-Release TLV 1 |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | |
- ~ ~
- | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-Withdraw-Release TLV n |
+ | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Optional Parameters |
+ | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
- Four octet integer used to identify this message.
-
- FEC-Withdraw-Release TLVs
- Each TLV specifies a FEC-label mapping being released. The encod-
- ing for the FEC-Withdraw-Release TLV is specified in Section "With-
- draw Message".
-
- NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
+ 32-bit value used to identify this message.
- Need to add multipath possibility to above by allowing multiple
- label TLVs to the FEC-label Mapping TLV. This will be done with
- the addition:
+ FEC TLV
+ Identifies the FEC for which the FEC-label mapping is being
+ released.
- Label TLV2 (optional)
- ...
- Label TLVn (optional)
+ Optional Parameters
+ This variable length field contains 0 or more parameters, each
+ encoded as a TLV. The optional parameters are:
- with discussion.
+ Optional Parameter Length Value
+ Label TLV variable See below
- END NOTE * END NOTE * END NOTE:
+ The encodings for Label TLVs are found in Section "Label TLVs".
- Optional Parameters
- No optional parameters are defined for the Label Release message.
+ Label
+ If present, the label being released (see procedures below).
-3.4.10.1. Label Release Message Procedures
+3.5.10.1. Label Release Message Procedures
- An LSR transmits a Release message to a peer when it is no longer
- needs a label previously received from or requested of that peer.
+ An LSR transmits a Label Release message to a peer when it is no
+ longer needs a label previously received from or requested of that
+ peer.
- An LSR transmits a Release message under any of the following condi-
- tions:
+ An LSR must transmit a Label Release message under any of the follow-
+ ing conditions:
1. The LSR which sent the label mapping is no longer the next hop
for the mapped FEC, and the LSR is configured for conservative
operation.
- 2. The LSR determines that a previously received label is no
- longer valid, as the downstream LSR from which it was received
- is no longer the next hop for the FEC, and the LSR is config-
- ured for conservative operation.
+ 2. The LSR receives a label mapping from an LSR which is not the
+ next hop for the FEC, and the LSR is configured for conserva-
+ tive operation.
- 3. The LSR has received a Withdraw message for a previously
+ 3. The LSR has received a Label Withdraw message for a previously
received label.
Note that if an LSR is configured for "liberal mode", a release mes-
sage will never be transmitted in the case of conditions (1) and (2)
as specified above. In this case, the upstream LSR keeps each unused
label, so that it can immediately be used later if the downstream
peer becomes the next hop for the FEC.
- The FEC in the FEC-Withdraw-Release TLV is a FEC for which labels are
- to be released. If no label TLV follows the FEC TLV, all labels
- associated with the FEC are to be released, else only the labels
- specified in the following Label TLV are to be released.
+ The FEC TLV specifies the FEC for which labels are to be released.
+ If no Label TLV follows the FEC, all labels associated with the FEC
+ are to be released; otherwise only the label specified in the
+ optional Label TLV is to be released.
-3.4.11. Label Query Message
+ The FEC TLV may contain the Wildcard FEC Element; if so, it may con-
+ tain no other FEC Elements. In this case, if the Label Release mes-
+ sage contains an optional Label TLV, then the label is to be released
+ for all FECs to which it is bound. If there is not an optional Label
+ TLV in the Label Release message, then the sending LSR is releasing
+ all label mappings previously learned from the receiving LSR.
- An LSR sends a Label Query message to an LDP peer when performing the
- loop prevention diffusion algorithm on an FEC.
+ See Appendx A "LDP Label Distribution Procedures" for more details.
- The encoding for the Label Query Message is:
+3.6. Messages and TLVs for Extensibility
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label Query (0x0405) | Message Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Message ID |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Path Vector TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Support for LDP extensibility includes the rules for the U and F bits
+ that specify how an LSR should handle unknown TLVs and messages.
- Message Id
- Four octet integer used to identify this message.
+ This section specifies TLVs and messages for vendor-private and
+ experimental use.
- The encodings for the FEC and Path Vector TLVs can be found in Sec-
- tion "Commonly Used TLVs".
+3.6.1. LDP Vendor-private Extensions
- Optional Parameters
- No optional parameters are defined for the Label Query message.
+ Vendor-private TLVs and messages are used to convey vendor-private
+ information between LSRs.
-3.4.11.1. Label Query Message Procecures
+3.6.1.1. LDP Vendor-private TLVs
- See Section "Loop Prevention via Diffusion" for general procedures
- for handling the Query Message.
+ The Type range 0x2F00 through 0x2FFF is reserved for vendor-private
+ TLVs.
-3.4.12. Explicit Route Request Message
+ The encoding for a vendor-private TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ER Request (0x0500) | Message Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Message ID |
+ |U|F| Type (0x2F00-0x2FFF) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-ER TLV 1 |
+ | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ | Data.... |
~ ~
| |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-ER TLV n |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Message Id
- Four octet integer used to identify this message.
-
- FEC-ER TLV
- Each specifies a binding between an FEC and a label. A FEC-ER TLV
- is a nested TLV that contains a FEC TLV, a Label TLV, an explicit-
- route identifier (ERLSPID) TLV, the explict-route TLV, an optional
- COS TLF, and an optional Bandwith Reservation TLV:
-
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC-ER TLV (0x0703) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | FEC TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ERLSPID TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Explicit Route TLV |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | COS TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bandwidth Reservation TLV (optional) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
- The encodings for the FEC and COS TLVs can be found in Section
- "Commonly Used TLVs".
-
- ERLSPID TLV
- The globally unique value that identifies the explicit route.
- The encoding for the ERLSPID is:
-
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ERLSPID (0x0801) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Explicit Identifier |
- + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
- | Peg Explicit Identifier |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
- Explicit Identifier
- A 6-octet globally unique value that identifies the explicit
- route LSP. It is generated by the LSR that creates the Expli-
- cit Request message. The first four octets is the LSR IP
- Address. The last two octets contain a `Local identifier'
- value. It is incumbent on an LSR that originates an Explicit
- Request message to choose an unused value for the Local Iden-
- tifier.
-
- Peg Explicit Identifier
- A 6-octet globally unique value that identifies a loose segment
- of an explicit route LSP. It is generated by the upstream peg
- LSR that creates the loose segment. The first four octets is
- the LSR IP Address. The last two octets contain a 'Local iden-
- tifier' value. It is incumbent on a peg LSR that creates a
- loose segment to choose an unused value for the Local Identif-
- ier every time the segment is reestablished. When a segment is
- strictly routed this field is set to zero by the sender and
- ignored by the receiver.
-
- Explicit Route TLV
- The sequence of ER Next Hop (ERNH) TLVs and a pointer to the one
- that should be processed by the LSR that receives this ER TLV.
- The encoding for the Explicit Route is:
-
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Explicit Route TLV (0x0800) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Next ERNH TLV Pointer | Reserved |P|Preempt|
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ERNH TLV (Variable length) |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
- Next ERNH TLV Pointer
- This 16 bit unsigned integer points to the offset in octets of
- the next ERNH TLV to be processed. The first octet after the
- two reserved octets that follow this pointer is defined to have
- an offset value of zero. For example an ERNH TLV Pointer value
- of zero would point to the first ERNH TLV in the sequence of
- ERNH Objects.
-
- P bit
- when set indicates that the loosely routed segments must remain
- pinned-down. ERLSP must be rerouted only when adjacency is
- lost along the segment. When not set indicates loose segment
- is not pinned down and must be changed to match the underlying
- hop-by-hop path.
-
- Preempt
- A 16 level preemption is provided to facilitate placement of
- ERLSP when resources aren't available. Each LSR maintains this
- value in the ERLSP control block. A higher preemption value
- can preempt LSPs with lower value.
-
- Reserved
- This field is reserved. It must be set to zero on transmission
- and must be ignored on receipt.
-
- ERNH TLV
- This TLV contains the four octet IP address of an LSR through
- which the Explicit Route LSP is to pass and an (optional)
- reservation (RES) TLV to be processed by that LSR.
-
- The strict TLV indicates that the ER LSP setup must be routed
- directly via the LSR indicated in the ERNH object; i.e. that
- that LSR must be the next hop in the Explicit Route LSP's path.
- The loose TLV indicates that the LSP may be routed in any way;
- i.e. via other unspecified LSRs, so long as it (eventually)
- reaches the LSR specified in the ERNH object. This TLV may be
- followed by the optional Reservation TLV.
+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- The ERNH encodings are:
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ER Strict TLV (0x0802) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | IPv4 Address |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ U bit
+ Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
+ (=0), a notification must be returned to the message originator and
+ the entire message must be ignored; if U is set (=1), the unknown
+ TLV is silently ignored and the rest of the message is processed as
+ if the unknown TLV did not exist.
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ER Loose TLV (0x0803) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | IPv4 Address |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ The determination as to whether a vendor-private message is under-
+ stood is based on the Type and the mandatory Vendor ID field.
- Ipv4 Address
- The IP address of the next LSR in the Explicit Route LSP.
+ F bit
+ Forward unknown TLV bit. This bit only applies when the U bit is
+ set and the LDP message containing the unknown TLF is is to be for-
+ warded. If F is clear (=0), the unknown TLV is not forwarded with
+ the containing message; if F is set (=1), the unknown TLV is for-
+ warded with the containing message.
- Bandwidth Reservation TLV
- Specifies the bandwidth reservation required at each LSR hop.
- The encoding for the Bandwidth Reservation is:
+ Type
+ Type value in the range 0x2F00 through 0x2FFF. Together, the Type
+ and Vendor Id field specify how the Data field is to be inter-
+ preted.
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bandwidth TLV (0x0804) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | BW requirement |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Length
+ Specifies the cumulative length in octets of the Vendor ID and Data
+ fields.
- BW Requirement
- Unsigned 32 bit integer representing the bandwidth, in units of
- kilo bps, that must be reserved for the LSP at every LSR identi-
- fied in the ERNH Object. The bandwidth is guaranteed within a
- coarser time period allowing for simpler implementations. The
- specified bandwidth is guaranteed within several milliseconds or
- a few seconds time period. Nodes may also use this as a minimal
- bandwidth guarantee within the same time period.
+ Vendor Id
+ 802 Vendor ID as assigned by the IEEE.
-3.4.12.1. Explicit Route Request Procedures
+ Data
+ The remaining octets after the Vendor ID in the Value field are
+ optional vendor-dependent data.
- See Sections "Explicitly Routing LSPs" and "ERLSP State Machine" for
- general procedures for handling the Explicit Route Request Message.
+3.6.1.2. LDP Vendor-private Messages
-3.4.13. Explicit Route Response Message
+ The Message Type range 0x2F00 through 0x2FFF is reserved for vendor-
+ private Messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ER Response (0x0501) | Message Length |
+ |U| Msg Type (0x2F00-0x2FFF) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ERLSPID TLV |
+ | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Label TLV |
+ + +
+ | Remaining Mandatory Parameters |
+ + +
+ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Status TLV |
+ | |
+ + +
+ | Optional Parameters |
+ + +
+ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- The encodings for the Label, and Status TLVs can be found in Section
- 3.3.3 ("Commonly Used TLVs").
+ U bit
+ Unknown message bit. Upon receipt of an unknown message, if U is
+ clear (=0), a notification is returned to the message originator;
+ if U is set (=1), the unknown message is silently ignored.
- Message Id
- Four octet integer used to identify this message.
+ The determination as to whether a vendor-private message is under-
+ stood is based on the Msg Type and the Vendor ID parameter.
- ERLSPID TLV
- The globally unique value used for ERLSPID in the Explicit Request
- message that elicited this Response message. The encoding for the
- ERLSPID (shown above and repeated here for convenience) is:
+ Msg Type
+ Message type value in the range 0x2F00 through 0x2FFF. Together,
+ the Msg Type and the Vendor ID specify how the message is to be
+ interpreted.
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ERLSPID (0x0801) | Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Explicit Identifier |
- + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | | |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
- | Peg Explicit Identifier |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Message Length
+ Specifies the cumulative length in octets of the Message ID, Vendor
+ ID, Remaining Mandatory Parameters and Optional Parameters.
- Explicit Identifier
- A 6-octet globally unique value that identifies the explicit
- route LSP. It is generated by the LSR that creates the Explicit
- Request message. The first four octets is the LSR IP Address.
- The last two octets contain a `Local identifier' value. It is
- incumbent on an LSR that originates an Explicit Request message
- to choose an unused value for the Local Identifier.
+ Message ID
+ 32-bit integer used to identify this message. Used by the sending
+ LSR to facilitate identifying notification messages that may apply
+ to this message. An LSR sending a notification message in response
+ to this message will include this Message Id in the notification
+ message; see Section "Notification Message".
- Peg Explicit Identifier
- A 6-octet globally unique value that identifies a loose segment
- of an explicit route LSP. It is generated by the upstream peg
- LSR that creates the loose segment. The first four octets is the
- LSR IP Address. The last two octets contain a 'Local identifier'
- value. It is incumbent on a peg LSR that creates a loose segment
- to choose an unused value for the Local Identifier every time the
- segment is reestablished. When a segment is strictly routed this
- field is set to zero by the sender and ignored by the receiver.
+ Vendor ID
+ 802 Vendor ID as assigned by the IEEE.
-3.4.13.1. Explicit Route Response Procedures
+ Remaining Mandatory Parameters
+ Variable length set of remaining required message parameters.
- See Sections "Explicitly Routing LSPs" and "ERLSP State Machine" for
- general procedures for handling the Explicit Response Request Mes-
- sage.
+ Optional Parameters
+ Variable length set of optional message parameters.
-3.5. Messages and TLVs for Extensibility
+3.6.2. LDP Experimental Extensions
- The procedures to provide for LDP extensiblity include rules for han-
- dling unknown messages and TLVs. The rules described in the sections
- that follow make use of the high order bits in the message or TLV
- type field. In these rules, "b" represents an arbitray bit value in
- a message or TLV type.
+ LDP support for experimentation is similar to support for vendor-
+ private extensions with the following differences:
-3.5.1. Procedures for Unknown Messages and TLVs
+ - The Type range 0x3F00 through 0x3FFF is reserved for experimental
+ TLVs.
-3.5.1.1. Unknown Message Types
+ - The Message Type range 0x3F00 through 0x3FFF is reserved for
+ experimental messages.
- When a message with an unknown Message Type is received, there are
- two possibilities as described below. The choice for how to handle
- an unknown Message Type is determined by the high-order bit of the
- Message Type field.
+ - The encodings for experimental TLVs and messages are similar to
+ the vendor-private encodings with the following difference.
- - Message Type = 0bbbbbbbbbbbbbbb
+ Experimental TLVs and messages use an Experiment ID field in
+ place of a Vendor ID field. The Experiment ID field is used with
+ the Type or Message Type field to specify the interpretation of
+ the experimental TLV or Message.
- The entire message must be rejected and the event signalled by a
- Notification Message with the Unknown Message Type Status Code.
+ Administration of Experiment IDs is the responsiblity of the
+ experimenters.
- - Message Type = 1bbbbbbbbbbbbbbb
+3.7. Message Summary
- The entire message must be dropped silently (i.e., it should be
- ignored and no error should be returned).
+ The following are the LDP messages defined in this version of the
+ protocol.
- In either case described above, an LSR that does not understand
- the message type must not attempt to process the message.
+ Message Name Type Section Title
-3.5.1.2. Unknown TLV in Known Message Type
+ Notification 0x0001 "Notification Message"
+ Hello 0x0100 "Hello Message"
+ Initialization 0x0200 "Initialization Message"
+ KeepAlive 0x0201 "KeepAlive Message"
+ Address 0x0300 "Address Message"
+ Address Withdraw 0x0301 "Address Withdraw Message"
+ Label Mapping 0x0400 "Label Mapping Message"
+ Label Request 0x0401 "Label Request Message"
+ Label Withdraw 0x0402 "Label Withdraw Message"
+ Label Release 0x0403 "Label Release Message"
+ Vendor-Private 0x2F00-0x2FFF
+ Experimental 0x3F00-0x3FFF
- When an unknown TLV is found in a known Message Type, there are three
- possibilities as described below. The choice for how to handle an
- unknown TLV is determined by the high-order two bits of the TLV Type
- field.
+3.8. TLV Summary
- - TLV Type = 0bbbbbbbbbbbbbbb
+ The following are the TLVs defined in this version of the protocol.
- The entire message must be rejected and the event signalled by a
- Notification Message with the Unknown TLV Status Code.
+ TLV Type Section Title
- - TLV Type = 10bbbbbbbbbbbbbb
+ FEC 0x0100 "FEC TLV"
+ Address List 0x0101 "Address List TLV"
+ COS 0x0102 "COS TLV"
+ Hop Count 0x0103 "Hop Count TLV"
+ Path Vector 0x0104 "Path Vector TLV"
+ Generic Label 0x0200 "Generic Label TLV"
+ ATM Label 0x0201 "ATM Label TLV"
+ Frame Relay Label 0x0202 "Frame Relay Label TLV"
+ Status 0x0300 "Status TLV"
+ Extended Status 0x0301 "Notification Message"
+ Returned PDU 0x0302 "Notification Message"
+ Returned Message 0x0303 "Notification Message"
+ Common Hello 0x0400 "Hello Message"
+ Parameters
+ Transport Address 0x0401 "Hello Message"
+ Configuration 0x0402 "Hello Message"
+ Sequence Number
+ Common Session 0x0500 "Initialization Message"
+ Parameters
+ ATM Session Parameters 0x0501 "Initialization Message"
+ Frame Relay Session 0x0502 "Initialization Message"
+ Parameters
+ Vendor-Private 0x2F00-0x2FFF
+ Experimental 0x3F00-0x3FFF
- The TLV must be dropped silently (i.e., it should be ignored and
- no error should be returned). If the semantics of the including
- Message Type dictate that message be forwarded to other nodes,
- the TLV must not be forwarded with the message.
+3.9. Status Code Summary
- - TLV Type = 11bbbbbbbbbbbbbb
+ The following are the Status Codes defined in this version of the
+ protocol.
- The TLV must be silently ignored (i.e., no error should be
- returned). If the semantics of the including Message Type dictate
- that message be forwarded to other nodes, the TLV must be for-
- warded unmodified with the message.
+ Status Code Type Section Title
-3.5.2. LDP Vendor-Private Extensions
+ Success 0x00000000 "Status TLV"
+ Bad LDP Identifer 0x80000001 "Events Signaled by ..."
+ Bad Protocol Version 0x80000002 "Events Signaled by ..."
+ Bad PDU Length 0x80000003 "Events Signaled by ..."
+ Unknown Message Type 0x80000004 "Events Signaled by ..."
+ Bad Message Length 0x80000005 "Events Signaled by ..."
+ Unknown TLV 0x80000006 "Events Signaled by ..."
+ Bad TLV length 0x80000007 "Events Signaled by ..."
+ Malformed TLV Value 0x80000008 "Events Signaled by ..."
+ Hold Timer Expired 0x80000009 "Events Signaled by ..."
+ Shutdown 0x8000000A "Events Signaled by ..."
+ Loop Detected 0x0000000B "Loop Detection"
+ Unknown FEC 0x0000000C "FEC Procedures"
+ No Route 0x0000000D "Label Request Mess ..."
+ No Label Resources 0x0000000E "Label Request Mess ..."
+ Label Resources Available 0x0000000F "Label Request Mess ..."
+ Session Rejected/ 0x80000010 "Session Initialization"
+ No Hello
+ Session Rejected/ 0x80000011 "Session Initialization"
+ Parameters Advertisement Mode
+ Session Rejected/ 0x80000012 "Session Initialization"
+ Parameters Max PDU Length
+ Session Rejected/ 0x80000013 "Session Initialization"
+ Parameters Label Range
- Both Vendor-Private Messages and Vendor-Private Objects are defined
- to convey vendor-private information or LDP extensions between LDP
- nodes. These extensions may also be useful for experimentation in
- existing networks.
+3.10. UDP and TCP Ports
-3.5.2.1. LDP Vendor-Private TLV
+ The UDP port for LDP Hello messages is 646.
- The following three Vendor-Private TLV classes are defined to be used
- in any message:
+ The TCP port for establishing LDP session connections is 646.
- - Vendor Private TLV Class 1. TLV type values:
+4. Security
- 0x3FXX (boolean 00111111bbbbbbbb)
+ This section specifies an optional mechanism to protect against the
+ introduction of spoofed TCP segments into LDP session connection
+ streams.
- - Vendor Private TLV Class 2. TLV type values:
+ It is based on use of the TCP MD5 Signature Option specified in
+ [rfc2385] for use by BGP. See [rfc1321] for a specification of the
+ MD5 hash function.
- 0xBFXX (boolean 10111111bbbbbbbb)
+4.1. The TCP MD5 Signature Option
- - Vendor Private TLV Class 3, TLV type values:
+ The following quotes from [rfc2385] outline the security properties
+ achieved by using the TCP MD5 Signature Option and summarizes its
+ operation:
- 0xFFXX (boolean 11111111bbbbbbbb)
+ "IESG Note
- These TLVs are to be handled according to the high order bit(s) of
- the TLV type. The unspecified part of the TLV type is assigned by
- the vendor and should be interpreted by a receiving LSR only if it
- understands the Vendor ID encoded in the TLV Value field.
+ This document describes currrent existing practice for securing
+ BGP against certain simple attacks. It is understood to have
+ security weaknesses against concerted attacks."
- The Value field of a Vendor Private TLV is defined as follows:
+ "Abstract
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vendor ID |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Data.... |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ This memo describes a TCP extension to enhance security for
+ BGP. It defines a new TCP option for carrying an MD5 [RFC1321]
+ digest in a TCP segment. This digest acts like a signature for
+ that segment, incorporating information known only to the con-
+ nection end points. Since BGP uses TCP as its transport, using
+ this option in the way described in this paper significantly
+ reduces the danger from certain security attacks on BGP."
- Vendor Id
- 802 Vendor ID as assigned by the IEEE.
+ "Introduction
- Data
- The remaining octets after the Vendor ID in the Value field
- are optional vendor-dependent data.
+ The primary motivation for this option is to allow BGP to pro-
+ tect itself against the introduction of spoofed TCP segments
+ into the connection stream. Of particular concern are TCP
+ resets.
-3.5.2.2. LDP Vendor-Private Messages
+ To spoof a connection using the scheme described in this paper,
+ an attacker would not only have to guess TCP sequence numbers,
+ but would also have had to obtain the password included in the
+ MD5 digest. This password never appears in the connection
+ stream, and the actual form of the password is up to the appli-
+ cation. It could even change during the lifetime of a particu-
+ lar connection so long as this change was synchronized on both
+ ends (although retransmission can become problematical in some
+ TCP implementations with changing passwords).
- The LDP Vendor-Private Message is carried in LDP PDUs to convey
- vendor-private information or LDP extensions between LSRs.
+ Finally, there is no negotiation for the use of this option in
+ a connection, rather it is purely a matter of site policy
+ whether or not its connections use the option."
- The following two Vendor-Private Message classes are defined:
+ "MD5 as a Hashing Algorithm
- - Vendor Private Message Class 1. Message type values:
+ Since this memo was first issued (under a different title), the
+ MD5 algorithm has been found to be vulnerable to collision
+ search attacks [Dobb], and is considered by some to be insuffi-
+ ciently strong for this type of application.
- 0x7FXX (boolean 01111111bbbbbbbb)
+ This memo still specifies the MD5 algorithm, however, since the
+ option has already been deployed operationally, and there was
+ no "algorithm type" field defined to allow an upgrade using the
+ same option number. The original document did not specify a
+ type field since this would require at least one more byte, and
+ it was felt at the time that taking 19 bytes for the complete
+ option (which would probably be padded to 20 bytes in TCP
+ implementations) would be too much of a waste of the already
+ limited option space.
- - Vendor Private Message Class 2. Message type values:
+ This does not prevent the deployment of another similar option
+ which uses another hashing algorithm (like SHA-1). Also, if
+ most implementations pad the 18 byte option as defined to 20
+ bytes anyway, it would be just as well to define a new option
+ which contains an algorithm type field.
- 0xFFXX (boolean 11111111bbbbbbbb)
+ This would need to be addressed in another document, however."
- The first TLV in a vendor private message must be the Vendor
- Private ID TLV, a Vendor Private Class 3 TLV, encoded as shown
- below:
+ End of quotes from [rfc2385].
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | 0xFF | 0x00 | 0x04 |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vendor ID |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+4.2. LDP Use of the TCP MD5 Signature Option
- Vendor-Private messages are to be handled according to the high
- order bit of the message type number. The determination as to
- whether the Vendor-Private message is understood is based on the
- Vendor ID in first TLV in the message body.
+ LDP uses the TCP MD5 Signature Option as follows:
-3.6. TLV Summary
+ - Use of the MD5 Signature Option for LDP TCP connections is a con-
+ figurable LSR option.
- The following are the TLVs defined in this version of the protocol.
+ - An LSR that uses the MD5 Signature Option is configured with a
+ password for each potential LDP peer.
- TLV Type Section Title
+ - The LSR applies the MD5 algorithm as specified in [RFC2385] to
+ compute the MD5 digest for a TCP segment to be sent to a peer.
+ This computation makes use of the peer password as well as the
+ TCP segment.
- FEC 0x0100 "FEC TLV"
- Address List 0x0101 "Address List TLV"
- COS 0x0102 "COS TLV"
- Hop Count 0x0103 "Hop Count TLV"
- Path Vector 0x0104 "Path Vector TLV"
- Generic Label 0x0200 "Generic Label TLV"
- ATM Label 0x0201 "ATM Label TLV"
- Frame Relay Label 0x0202 "Frame Relay Label TLV"
- Status 0x0300 "Status TLV"
- Extended Status 0x0301 "Notification Message"
- Targeted Hello 0x0400 "Hello Message"
- Send Targeted Hello 0x0401 "Hello Message"
- Transport Address 0x0402 "Hello Message"
- Hello Hold Time 0x0403 "Hello Message"
- Common Session 0x0500 "Initialization Message"
- Parameters
- Label Allocation 0x0501 "Initialization Message"
- Discipline
- Loop Detection 0x0502 "Initialization Message"
- Merge 0x0503 "Initialization Message"
- ATM Null Encapsulation 0x0504 "Initialization Message"
- ATM Label Range 0x0600 "Initialization Message"
- Frame Relay Label Range 0x0601 "Initialization Message"
- FEC-Label Mapping 0x0700 "Label Mapping Message"
- FEC-Request 0x0701 "Label Request Message"
- FEC-Withdraw-Release 0x0702 "Label Withdraw Message"
- FEC-ER TLV 0x0703 "Explicit Request Message"
- Explicit Route 0x0800 "Explicit Request Message"
- ERLSPID 0x0801 "Explicit Request Message"
- ER Strict 0x0802 "Explicit Request Message"
- ER Loose 0x0803 "Explicit Request Message"
- Bandwidth 0x0804 "Explicit Request Message"
+ - When the LSR receives a TCP segment with an MD5 digest, it vali-
+ dates the segment by calculating the MD5 digest (using its own
+ record of the password) and compares the computed digest with the
+ received digest. If the comparison fails, the segment is dropped
+ without any response to the sender.
-3.7. Status Code Summary
+ - The LSR ignores LDP Hellos from any LSR for which a password has
+ not been configured. This ensures that the LSR establishes LDP
+ TCP connections only with LSRs for which a password has been con-
+ figured.
- The following are the Status Codes defined in this version of the
- protocol.
+5. Intellectual Property Considerations
- Status Code Type Section Title
+ The IETF has been notified of intellectual property rights claimed in
+ regard to some or all of the specification contained in this docu-
+ ment. For more information consult the online list of claimed
+ rights.
- Success 0x0000 "Status TLV"
- Bad LDP Identifer 0x8001 "Events Signalled by ..."
- Bad Protocol Version 0x8002 "Events Signalled by ..."
- Bad PDU Length 0x8003 "Events Signalled by ..."
- Unknown Message Type 0x8004 "Events Signalled by ..."
- Bad Message Length 0x8005 "Events Signalled by ..."
- Unknown TLV 0x8006 "Events Signalled by ..."
- Bad TLV length 0x8007 "Events Signalled by ..."
- Malformed TLV Value 0x8008 "Events Signalled by ..."
- Hold Timer Expired 0x8009 "Events Signalled by ..."
- Shutdown 0x000A "Events Signalled by ..."
- Loop Detected 0x000B "Loop Detection Via Diffusion"
+6. Acknowledgments
-4. Security
+ The ideas and text in this document have been collected from a number
+ of sources. We would like to thank Rick Boivie, Ross Callon, Alex
+ Conta, Eric Gray, Yoshihiro Ohba, Eric Rosen, Bernard Suter, Yakov
+ Rekhter, and Arun Viswanathan.
- Security considerations will be addressed in a future revision of
- this document.
+7. References
-5. Acknowledgments
+ [ARCH] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label
+ Switching Architecture", draft-ietf-mpls-arch-02.txt, July 1998
- The ideas and text in this document have been collected from a number
- of sources. We would like to thank Rick Boivie, Ross Callon, Alex
- Conta, Eric Rosen, Bernard Suter, Yakov Rekhter, and Arun
- Viswanathan.
+ [ATM] B. Davie, J. Lawrence, K. McCloghrie, Y. Rekhter, E. Rosen, G.
+ Swallow, P. Doolan, "Use of Label Switching With ATM", draft-ietf-
+ mpls-atm-00.txt, September, 1998
-6. References
+ [DIFFSERV] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W.
+ Weiss, "An Architecture for Differentiated Services", draft-ietf-
+ diffserv-arch-02.txt, October, 1998
- [FRAMEWORK] Callon et al, "A Framework for Multiprotocol Label
- Switching" draft-ietf-mpls-framework-01.txt, July 1997
+ [ENCAP] E. Rosen, Y. Rekhter, D. Tappan, D. Farinacci, G. Fedorkow,
+ T. Li, A. Conta, "MPLS Label Stack Encoding" draft-ietf-mpls-label-
+ encaps-02.txt, July, 1998
- [ARCH] Rosen et al, "A Proposed Architecture for MPLS" draft-ietf-
- mpls-arch-02.txt, July 1998
+ [FR] A. Conta, P. Doolan, A. Malis, "Use of Label Switching on Frame
+ Relay Networks" draft-ietf-mpls-fr-02.txt, October, 1998
+ [FRAMEWORK] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swal-
+ low, A. Viswanathan, "A Framework for Multiprotocol Label Switching"
+ draft-ietf-mpls-framework-02.txt, November 1997
- [ENCAP] Farinacci et al, "MPLS Label Stack Encoding" draft-ietf-
- mpls-label-encaps-02.txt, July, 1998
+ [rfc1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321,
+ April 1992.
- [FR] Conta et al, "Use of Label Switching on Frame Relay Networks"
- draft-ietf-mpls-fr-01.txt, August, 1998
+ [rfc1483] J. Heinanen, "Multiprotocol Encapsulation over ATM Adapta-
+ tion Layer 5", RFC 1483, Telecom Finland, July 1993
[rfc1583] J. Moy, "OSPF Version 2", RFC 1583, Proteon Inc, March 1994
+ [rfc1700] J. Reynolds, J.Postel, "ASSIGNED NUMBERS", October 1994.
+
[rfc1771] Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, IBM Corp, Cisco Systems, March 1995
- [rfc1483] J. Heinanen, "Multiprotocol Encapsulation over ATM Adapta-
- tion Layer 5", RFC 1483, Telecom Finland, July 1993
+ [rfc2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
+ Signature Option", RFC 2385, August 1998.
-7. Author Information
+8. Author Information
Loa Andersson
- Bay Networks Inc
- 3 Federal Street
- Billerica, MA 01821
- email: Loa_Andersson@baynetworks.com
+ Nortel Networks Inc
+ Kungsgatan 34, PO Box 1788
+ 111 97 Stockholm
+ Sweden
+ Phone: +46 8 441 78 34, Mobile: +46 70 522 78 34
+ email: loa_andersson@baynetworks.com
Paul Doolan
Ennovate Networks
330 Codman Hill Rd
Marlborough MA 01719
Phone: 978-263-2002
email: pdoolan@ennovatenetworks.com
Nancy Feldman
IBM Corp.
17 Skyline Drive
Hawthorne NY 10532
Phone: 914-784-3254
email: nkf@us.ibm.com
Andre Fredette
- Bay Networks Inc
+ Nortel Networks Inc
3 Federal Street
Billerica, MA 01821
Phone: 978-916-8524
email: fredette@baynetworks.com
Bob Thomas
Cisco Systems, Inc.
250 Apollo Dr.
Chelmsford, MA 01824
Phone: 978-244-8078
email: rhthomas@cisco.com
+
+Appendix A. LDP Label Distribution Procedures
+
+ This section specifies label distribution behavior in terms of LSR
+ response to the following events:
+
+ - Receive Label Request Message;
+ - Receive Label Mapping Message;
+ - Receive Label Release Message;
+ - Receive Label Withdraw Message;
+ - Recognize new FEC;
+ - Detect change in FEC next hop;
+ - Receive Notification Message / No Label Resources;
+ - Receive Notification Message / No Route;
+ - Receive Notification Message / Loop Detected;
+ - Receive Notification Message / Label Resources Available;
+ - Detect local label resources have become available;
+ - LSR decides to no longer label switch a FEC;
+ - Timeout of deferred label request.
+
+ The specification of LSR behavior in response to an event has three
+ parts:
+
+ 1. Summary. Prose that describes LSR response to the event in
+ overview.
+
+ 2. Context. A list of elements referred to by the Algorithm part
+ of the specification. (See 3.)
+
+ 3. Algorithm. An algorithm for LSR response to the event.
+
+ The Summary may omit details of the LSR response, such as bookkeeping
+ action or behavior dependent on the LSR label advertisement mode,
+ control mode, or label retention mode in use. The intent is that the
+ Algorithm fully and unambiguously specify the LSR response.
+
+ The algorithms in this section use procedures defined in the MPLS
+ architecture specification [ARCH] for hop-by-hop routed traffic.
+ These procedures are:
+
+ - Label Distribution procedure, which is performed by a downstream
+ LSR to determine when to distribute a label for a FEC to LDP
+ peers. The architecture defines four Label Distribution pro-
+ cedures:
+
+ . Downstream Unsolicited Independent Control, called PushUncon-
+ ditional in [ARCH].
+
+ . Downstream Unsolicited Ordered Control, called PushCondi-
+ tional in [ARCH].
+
+ . Downstream On Demand Independent Control, called PulledUncon-
+ ditional in [ARCH].
+
+ . Downstream On Demand Ordered Control, called PulledCondi-
+ tional in [ARCH].
+
+ - Label Withdrawal procedure, which is performed by a downstream
+ LSR to determine when to withdraw a FEC label mapping previously
+ distributed to LDP peers. The architecture defines a single Label
+ Withdrawal procedure. Whenever an LSR breaks the binding between
+ a label and a FEC, it must withdraw the FEC label mapping from
+ all LDP peers to which it has previously sent the mapping.
+
+ - Label Request procedure, which is performed by an upstream LSR to
+ determine when to explicitly request that a downstrem LSR bind a
+ label to a FEC and send it the corresponding label mapping. The
+ architecture defines three Label Request procedures:
+
+ . Request Never. The LSR never requests a label.
+
+ . Request When Needed. The LSR requests a label whenever it
+ needs one.
+
+ . Request On Request. This procedure is used by non-label merg-
+ ing LSRs. The LSR requests a label when it receives a request
+ for one, in addition to whenever it needs one.
+
+ - Label Release procedure, which is performed by an upstream LSR to
+ determine when to release a previously received label mapping for
+ a FEC. The architecture defines two Label Release procedures:
+
+ . Conservative label retention, called Release On Change in
+ [ARCH].
+
+ . Liberal label retention, called No Release On Change in
+ [ARCH].
+
+ - Label Use procedure, which is performed by an LSR to determine
+ when to start using a FEC label for forwarding/switching. The
+ architecture defines three Label Use procedures:
+
+ . Use Immediate. The LSR immediately uses a label received from
+ a FEC next hop for forwarding/switching.
+
+ . Use If Loop Free. The LSR uses a FEC label received from a
+ FEC next hop for forwarding/switching only if it has deter-
+ mined that by doing so it will not cause a forwarding loop.
+
+ . Use If Loop Not Detected. This procedure is the same as Use
+ Immediate unless the LSR has detected a loop in the FEC LSP.
+ Use of the FEC label for forwarding/switching will continue
+ until the next hop for the FEC changes or the loop is no
+ longer detected.
+
+ This version of LDP does not include a loop prevention mechanism;
+ therefore, the procedures below do not make use of the Use If
+ Loop Free procedure.
+
+ - Label No Route procedure (called Label Not Available procedure in
+ [ARCH]), which is performed by an upstream LSR to determine how
+ to respond to a No Route notification from a downstream LSR in
+ response to a request for a FEC label mapping. The architecture
+ specification defines two Label No Route procedures:
+
+ . Request Retry. The LSR should issue the label request at a
+ later time.
+
+ . No Request Retry. The LSR should assume the downstream LSR
+ will provide a label mapping when the downstream LSR has a
+ next hop and it should not reissue the request.
+
+A.1. Handling Label Distribution Events
+
+ The algorithms for handling label distribution events share common
+ actions. The specifications below package these common actions into
+ procedure units. Specifications for these common procedures are in
+ their own section "Common Label Distribution Procedures", which fol-
+ lows this.
+
+ An implementation would use data structures to store information
+ about protocol activity. This appendix specifies the information to
+ be stored in sufficient detail to describe the algorithms, and
+ assumes the ability to retrieve the information as needed. It does
+ not specify the details of the data structures.
+
+A.1.1. Receive Label Request
+
+ Summary:
+
+ The response by an LSR to receipt of a FEC label request from an
+ LDP peer may involve one or more of the following actions:
+
+ - Transmission of a notification message to the requesting LSR
+ indicating why a label mapping for the FEC cannot be provided;
+
+ - Transmission of a FEC label mapping to the requesting LSR;
+
+ - Transmission of a FEC label request to the FEC next hop;
+
+ - Installation of labels for forwarding/switching use by the LSR.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - MsgSource. The LDP peer that sent the message.
+
+ - FEC. The FEC specified in the message.
+
+ - RAttributes. Attributes received with the message. E.g., CoS, Hop
+ Count Path Vector.
+
+ - SAttributes. Attributes to be included in Label Request message,
+ if any, propagated to FEC Next Hop.
+
+ - StoredHopCount. The hop count, if any, previously recorded for
+ the FEC.
+
+ Algorithm:
+
+ LRq.1 Execute procedure Check_Received_Attributes (MsgSource, RAt-
+ tributes).
+ If Loop Detected, goto LRq.11.
+
+ LRq.2 Is there a Next Hop for FEC?
+ If so, goto LRq.4.
+
+ LRq.3 Execute procedure Send_Notification (MsgSource, No Route).
+ Goto LRq.11.
+
+ LRq.4 Has LSR previously received a label request for FEC from
+ MsgSource?
+ If not, goto LRq.6. (See Note 1.)
+ LRq.5 Is the label request a duplicate request?
+ If so, Goto LRq.11. (See Note 2.)
+
+ LRq.6 Record label request for FEC received from MsgSource and mark
+ it pending.
+
+ LRq.7 Perform LSR Label Distribution procedure:
+
+ For Downstream Unsolicited Independent Control OR
+ For Downstream On Demand Independent Control
+
+ 1. Has LSR previously received and retained a label map-
+ ping for FEC from Next Hop?.
+ Is so, set Propagating to IsPropagating.
+ If not, set Propagating to NotPropagating.
+
+ 2. Execute procedure
+ Prepare_Label_Mapping_Attributes(MsgSource, FEC, RAt-
+ tributes, SAttributes, Propagating, StoredHopCount).
+
+ 3. Execute procedure Send_Label (MsgSource, FEC, SAttri-
+ butes).
+
+ 4. Is LSR egress for FEC? OR
+ Has LSR previously received and retained a label map-
+ ping for FEC from Next Hop?
+ If so, goto LRq.9. If not, goto LRq.8.
+
+ For Downstream Unsolicited Ordered Control OR
+ For Downstream On Demand Ordered Control
+
+ 1. Is LSR egress for FEC? OR
+ Has LSR previously received and retained a label map-
+ ping for FEC from Next Hop?
+ If not, goto LRq.8.
+
+ 2. Execute procedure
+ Prepare_Label_Mapping_Attributes(MsgSource, FEC, RAt-
+ tributes, SAttributes, IsPropagating, StoredHopCount)
+
+ 3. Execute procedure Send_Label (MsgSource, FEC, SAttri-
+ butes).
+ Goto LRq.9.
+
+ LRq.8 Perform LSR Label Request procedure:
+
+ For Request Never
+ 1. Goto LRq.11.
+
+ For Request When Needed OR
+ For Request On Request
+
+ 1. Execute procedure Prepare_Label_Request_Attributes
+ (Next Hop, FEC, RAttributes, SAttributes);
+
+ 2. Execute procedure Send_Label_Request (Next Hop, FEC,
+ SAttributes).
+ Goto LRq.11.
+
+ LRq.9 Has LSR successfully sent a label for FEC to MsgSource?
+ If not, goto LRq.11. (See Note 3.)
+
+ LRq.10 Perform LSR Label Use procedure.
+
+ For Use Immediate OR
+ For Use If Loop Not Detected
+
+ 1. Install label sent to MsgSource and label from Next
+ Hop (if LSR is not egress) for forwarding/switching
+ use.
+
+ LRq.11 DONE
+
+ Notes:
+
+ 1. In the case where MsgSource is a non-label merging LSR it will
+ send a label request for each upstream LDP peer that has
+ requested a label for FEC from it. The LSR must be able to dis-
+ tinguish such requests from a non-label merging MsgSource from
+ duplicate label requests.
+
+ 2. When an LSR sends a label request to a peer it records that the
+ request has been sent and marks it as outstanding. As long as
+ the request is marked outstanding the LSR should not send
+ another request for the same label to the peer. Such a second
+ request would be a duplicate. The Send_Label_Request procedure
+ described below obeys this rule.
+
+ A duplicate label request is considered a protocol error and
+ should be dropped by the receiving LSR (perhaps with a suitable
+ notification returned to MsgSource).
+
+ 3. The Send_Label procedure may fail due to lack of label
+ resources, in which case the LSR should not perform the Label
+ Use procedure.
+
+A.1.2. Receive Label Mapping
+
+ Summary:
+
+ The response by an LSR to receipt of a FEC label mapping from an
+ LDP peer may involve one or more of the following actions:
+
+ - Transmission of a label release message for the FEC label to the
+ LDP peer;
+
+ - Transmission of label mapping messages for the FEC to one or more
+ LDP peers,
+
+ - Installation of the newly learned label for forwarding/switching
+ use by the LSR.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - MsgSource. The LDP peer that sent the message.
+
+ - FEC. The FEC specified in the message.
+
+ - Label. The label specified in the message.
+
+ - PrevAdvLabel. The label for FEC, if any, previously advertised to
+ an upstream peer.
+
+ - StoredHopCount. The hop count previously recorded for the FEC.
+
+ - RAttributes. Attributes received with the message. E.g., CoS, Hop
+ Count, Path Vector.
+
+ - SAttributes to be included in Label Mapping message, if any, pro-
+ pagated to upstream peers.
+
+ Algorithm:
+
+ LMp.1 Does the received label mapping match an outstanding label
+ request for FEC previously sent to MsgSource.
+ If not, goto LMp.9.
+
+ LMp.2 Delete record of outstanding FEC label request.
+
+ LMp.3 Execute procedure Check_Received_Attributes (MsgSource, RAt-
+ tributes).
+ If No Loop Detected, goto LMp.9.
+
+ LMp.4 Does the LSR have a previously received label mapping for FEC
+ from MsgSource?
+ If not, goto LMp.8. (See Note 1.).
+
+ LMp.5 Does the label previously received from MsgSource match Label
+ (i.e., the label received in the message)?
+ If not, goto LMp.8. (See Note 2.)
+
+ LMp.6 Delete matching label mapping for FEC previously received
+ from MsgSource.
+
+ LMp.7 Remove Label from forwarding/switching use. (See Note 3.).
+
+ LMp.8 Execute procedure Send_Message (MsgSource, Label Release,
+ FEC, Label). Goto LMp.26.
+
+ LMp.9 Determine the Next Hop for FEC.
+
+ LMp.10 Is MsgSource the Next Hop for FEC?
+ If so, goto LMp.12.
+
+ LMp.11 Perform LSR Label Release procedure:
+
+ For Conservative Label retention:
+
+ 1. Execute procedure Send_Message (MsgSource, Label
+ Release, FEC, Label).
+ Goto LMp.26.
+
+ For Liberal Label retention:
+
+ 1. Record label mapping for FEC with Label and RAttri-
+ butes has been received from MsgSource.
+ Goto LMp.26.
+
+ LMp.12 Does LSR have a previously received label mapping for FEC
+ from MsgSource?
+ If not, goto LMp.14
+
+ LMp.13 Does the label previously received from MsgSource match Label
+ (i.e., the label received in the message)?
+ If not, goto LMp.8. (See Note 2.)
+ LMp.14 Is LSR an ingress for FEC?
+ If not, goto LMp.16.
+
+ LMp.15 Install Label for forwarding/switching use.
+
+ LMp.16 Record label mapping for FEC with Label and RAttributes has
+ been received from MsgSource.
+
+ LMp.17 Iterate through for LMp.25 for each Peer, other than
+ MsgSource.
+
+ LMp.18 Has LSR previously sent a label mapping for FEC to Peer?
+ If not, goto LMp.23.
+
+ LMp.19 Are RAttributes in the received label mapping consistent with
+ those previously sent to Peer?
+ If so, goto LMp.24. (See Note 4.)
+
+ LMp.20 Execute procedure Prepare_Label_Mapping_Attributes(Peer, FEC,
+ RAttributes, SAttributes, IsPropagating, StoredHopCount).
+
+ LMp.21 Execute procedure Send_Message (Peer, Label Mapping, FEC,
+ PrevAdvLabel, SAttributes). (See Note 5.)
+
+ LMp.22 Update record of label mapping for FEC previously sent to
+ Peer to include the new attributes sent.
+ Goto LMp.24.
+
+ LMp.23 Perform LSR Label Distribution procedure:
+
+ For Downstream Unsolicited Independent Control OR
+ For Downstream Unsolicited Ordered Control
+
+ 1. Execute procedure
+ Prepare_Label_Mapping_Attributes(Peer, FEC, RAttri-
+ butes, SAttributes, IsPropagating, UnknownHopCount).
+
+ 2. Execute procedure Send_Label (Peer, FEC, SAttri-
+ butes).
+ If the procedure fails, continue iteration for next
+ Peer at LMp.17.
+
+ 3. Goto LMp.24.
+
+ For Downstream On Demand Independent Control OR
+ For Downstream On Demand Ordered Control
+
+ 1. Does LSR have a label request for FEC from Peer
+ marked as pending?
+ If not, continue iteration for next Peer at LMp.17.
+
+ 2. Execute procedure
+ Prepare_Label_Mapping_Attributes(Peer, FEC, RAttri-
+ butes, SAttributes, IsPropagating, UnknownHopCount)
+
+ 3. Execute procedure Send_Label (Peer, FEC, SAttri-
+ butes).
+ If the procedure fails, continue iteration for next
+ Peer at LMp.17.
+
+ 4. Goto LMp.24.
+
+ LMp.24 Perform LSR Label Use procedure:
+
+ For Use Immediate OR
+ For Use If Loop Not Detected
+
+ 1. Install label received and label sent to Peer for
+ forwarding/switching use.
+ Goto LMp.25.
+
+ LMp.25 End iteration from LMp.17.
+
+ LMp.26 DONE.
+
+ Notes:
+
+ 1. If LSR has detected a loop and it has not previously received a
+ label mapping from MsgSource for the FEC, it simply releases
+ the label.
+
+ 2. A mapping with a different label from the same peer would be an
+ attempt to establish multipath label switching, which is not
+ supported in this version of LDP.
+
+ 3. If Label is not in forwarding/switching use, LMp.7 has no
+ effect.
+
+ 4. The loop detection Path Vector attribute is considered in this
+ check. If the received RAttributes include a Path Vector and
+ no Path Vector had been previously sent to the Peer, or if the
+ received Path Vector is inconsistent with the Path Vector pre-
+ viously sent to the Peer, then the attributes are considered to
+ be inconsistent. Note that an LSR is not required to store a
+ received Path Vector after it propagates the Path Vector in a
+ mapping message. If an LSR does not store the Path Vector, it
+ has no way to check the consistency of a newly received Path
+ Vector. This means that whenever such an LSR receives a map-
+ ping message carrying a Path Vector it must always propagate
+ the Path Vector.
+
+ 5. LMp.19 through LMp.21 deal with a situation that can arise when
+ the LSR is using independent control and it receives a mapping
+ from the downstream peer after it has sent a mapping to an
+ upstream peer. In this situation the LSR needs to propagate any
+ changed attributes, such as Hop Count, upstream. If Loop Detec-
+ tion is configured on, the propagated attributes must include
+ the Path Vector
+
+A.1.3. Receive Label Release
+
+ Summary:
+
+ When an LSR receives a label release message for a FEC from a peer,
+ it checks whether other peers hold the released label. If none do,
+ the LSR removes the label from forwarding/switching use, if it has
+ not already done so, and if the LSR holds a label mapping from the
+ FEC next hop, it releases the label mapping.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - MsgSource. The LDP peer that sent the message.
+
+ - Label. The label specified in the message.
+
+ - FEC. The FEC specified in the message.
+
+ Algorithm:
+
+ LRl.1 Remove MsgSource from record of peers that hold Label for
+ FEC. (See Note 1.)
+
+ LRl.2 Does message match an outstanding label withdraw for FEC pre-
+ viously sent to MsgSource?
+ If not, goto LRl.4
+
+ LRl.3 Delete record of outstanding label withdraw for FEC previ-
+ ously sent to MsgSource.
+
+ LRl.4 Is LSR merging labels for this FEC?
+ If not, goto LRl.6. (See Note 2.)
+ LRl.5 Has LSR previously advertised a label for this FEC to other
+ peers?
+ If so, goto LRl.10.
+
+ LRl.6 Is LSR egress for the FEC?
+ If so, goto LRl.10
+
+ LRl.7 Is there a Next Hop for FEC? AND
+ Does LSR have a previously received label mapping for FEC
+ from Next Hop?
+ If not, goto LRl.10.
+
+ LRl.8 Is LSR configured to propagate releases?
+ If so, goto LRl.10. (See Note 3.)
+
+ LRl.9 Execute procedure Send_Message (Next Hop, Label Release, FEC,
+ Label from Next Hop).
+
+ LRl.10 Remove Label from forwarding/switching use for traffic from
+ MsgSource.
+
+ LRl.11 Do any peers still hold Label for FEC?
+ If so, goto LRl.13.
+
+ LRl.12 Free the Label.
+
+ LRl.13 DONE.
+
+ Notes:
+
+ 1. If LSR is using Downstream Unsolicted label distribution, it
+ should not re-advertise a label mapping for FEC to MsgSource
+ until MsgSource requests it.
+
+ 2. LRl.4 through LRl.8 deal with determining whether where the LSR
+ should propagate the label release to a downstream peer
+ (LRl.9).
+
+ 3. If LRl.8 is reached, no upstream LSR holds a label for the FEC,
+ and the LSR holds a label for the FEC from the FEC Next Hop.
+ The LSR could propagate the Label Release to the Next Hop. By
+ propagating the Label Release the LSR releases a potentially
+ scarce label resource. In doing so, it also increases the
+ latency for re-establishing the LSP should MsgSource or some
+ other upstream LSR send it a new Label Request for FEC.
+
+ Whether or not to propagate the release is not a protocol
+ issue. Label distribution will operate properly whether or not
+ the release is propagated. The decision to propagate or not
+ should take into consideration factors such as: whether labels
+ are a scarce resource in the operating environment; the impor-
+ tance of keeping LSP setup latency low by keeping the amount of
+ signalling required small; whether LSP setup is ingress-
+ controlled or egress-controlled in the operating environment.
+
+A.1.4. Receive Label Withdraw
+
+ Summary:
+
+ When an LSR receives a label withdraw message for a FEC from an LDP
+ peer, it responds with a label release message and it removes the
+ label from any forwarding/switching use. If ordered control is in
+ use, the LSR sends a label withdraw message to each LDP peer to
+ which it had previously sent a label mapping for the FEC. If the
+ LSR is using Downstream on Demand label advertisement with indepen-
+ dent control, it then acts as if it had just recognized the FEC.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - MsgSource. The LDP peer that sent the message.
+
+ - Label. The label specified in the message.
+
+ - FEC. The FEC specified in the message.
+
+ Algorithm:
+
+ LWd.1 Remove Label from forwarding/switching use. (See Note 1.)
+
+ LWd.2 Execute procedure Send_Message (MsgSource, Label Release,
+ FEC, Label)
+
+ LWd.3 Has LSR previously received and retained a matching label
+ mapping for FEC from MsgSource?
+ If not, goto LWd.13.
+
+ LWd.4 Delete matching label mapping for FEC previously received
+ from MsgSource.
+
+ LWd.5 Is LSR using ordered control?
+ If so, goto LWd.8.
+
+ LWd.6 Is MsgSource using Downstream On Demand label advertisement?
+ If not, goto LWd.13.
+
+ LWd.7 Generate Event: Recognize New FEC for FEC.
+ Goto LWd.13. (See Note 2.)
+
+ LWd.8 Iterate through LWd.12 for each Peer, other than MsgSource.
+
+ LWd.9 Has LSR previously sent a label mapping for FEC to Peer?
+ If not, continue interation for next Peer at LWd.8.
+
+ LWd.10 Does the label previously sent to Peer "map" to the withdrawn
+ Label?
+ If not, continue iteration for next Peer at LWd.8. (See Note
+ 3.)
+
+ LWd.11 Execute procedure Send_Label_Withdraw (Peer, FEC, Label pre-
+ viously sent to Peer).
+
+ LWd.12 End iteration from LWd.8.
+
+ LWd.13 DONE
+
+ Notes:
+
+ 1. If Label is not in forwarding/switching use, LWd.1 has no
+ effect.
+
+ 2. LWd.7 handles the case where the LSR is using Downstream On
+ Demand label distribution with independent control. In this
+ situation the LSR should send a label request to the FEC next
+ hop as if it had just recognized the FEC.
+
+ 3. LWd.10 handles both label merging (one or more incoming labels
+ map to the same outgoing label) and no label merging (one label
+ maps to the outgoing label) cases.
+
+A.1.5. Recognize New FEC
+
+ Summary:
+
+ The response by an LSR to learning a new FEC may involve one or
+ more of the following actions:
+
+ - Transmission of label mappings for the FEC to one or more LDP
+ peers;
+ - Transmission of a label request for the FEC to the FEC next hop;
+
+ - Any of the actions that can occur when the LSR receives a label
+ mapping for the FEC from the FEC next hop.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - FEC. The newly recognized FEC.
+
+ - Next Hop. The next hop for the FEC.
+
+ - InitAttributes. Attributes to be associated with the new FEC.
+ (See Note 1.)
+
+ - SAttributes. Attributes to be included in Label Mapping or Label
+ Request messages, if any, sent to peers.
+
+ - StoredHopCount. Hop count associated with FEC label mapping , if
+ any, previously received from Next Hop.
+
+ Algorithm:
+
+ FEC.1 Perform LSR Label Distribution procedure:
+
+ For Downstream Unsolicited Independent Control
+
+ 1. Iterate through 5 for each Peer.
+
+ 2. Has LSR previously received and retained a label map-
+ ping for FEC from Next Hop?
+ If so, set Propagating to IsPropagating.
+ If not, set Propagating to NotPropagating.
+
+ 3. Execute procedure Prepare_Label_Mapping_Attributes
+ (Peer, FEC, InitAttributes, SAttributes, Propagating,
+ Unknown hop count(0)).
+
+ 4. Execute procedure Send_Label (Peer, FEC, SAttributes)
+
+ 5. End iteration from 1.
+ Goto FEC.2.
+
+ For Downstream Unsolicited Ordered Control
+
+ 1. Iterate through 5 for each Peer.
+
+ 2. Is LSR egress for the FEC? OR
+ Has LSR previously received and retained a label map-
+ ping for FEC from Next Hop?
+ If not, continue iteration for next Peer.
+
+ 3. xecute procedure Prepare_Label_Mapping_Attributes
+ (Peer, FEC, InitAttributes, SAttributes, Propagating,
+ StoredHopCount).
+
+ 4. Execute procedure Send_Label (Peer, FEC, SAttributes)
+
+ 5. End iteration from 1.
+ Goto FEC.2.
+
+ For Downstream On Demand Independent Control OR
+ For Downstream On Demand Ordered Control
+
+ 1. Goto FEC.2. (See Note 2.)
+
+ FEC.2 Has LSR previously received and retained a label mapping for
+ FEC from Next Hop?
+ If so, goto FEC.5
+
+ FEC.3 Is Next Hop an LDP peer?
+ If not, Goto FEC.6
+
+ FEC.4 Perform LSR Label Request procedure:
+
+ For Request Never
+
+ 1. Goto FEC.6
+
+ For Request When Needed OR
+ For Request On Request
+
+ 1. Execute procedure Prepare_Label_Request_Attributes
+ (Next Hop, FEC, InitAttributes, SAttributes);
+
+ 2. Execute procedure Send_Label_Request (Next Hop, FEC,
+ SAttributes).
+ Goto FEC.6.
+
+ FEC.5 Generate Event: Received Label Mapping from Next Hop. (See
+ Note 3.)
+
+ FEC.6 DONE.
+
+ Notes:
+
+ 1. An example of an attribute that might be part of InitAttributes
+ is CoS. The means by which FEC InitAttributes, if any, are
+ specified is beyond the scope of LDP. Note that the InitAttri-
+ butes will not include a known Hop Count or a Path Vector.
+
+ 2. An LSR using Downstream On Demand label distribution would send
+ a label only if it had a previously received label request
+ marked as pending. The LSR would have no such pending requests
+ because it responds to any label request for an unknown FEC by
+ sending the requesting LSR a No Route notification and discard-
+ ing the label request; see LRq.3
+
+ 3. If the LSR has a label for the FEC from the Next Hop, it should
+ behave as if it had just received the label from the Next Hop.
+ This occurs in the case of Liberal label retention mode.
+
+A.1.6. Detect change in FEC next hop
+
+ Summary:
+
+ The response by an LSR to a change in the next hop for a FEC may
+ involve one or more of the following actions:
+
+ - Removal of the label from the FEC's old next hop from
+ forwarding/switching use;
+
+ - Transmission of label mappping messages for the FEC to one or
+ more LDP peers;
+
+ - Transmission of a label request to the FEC's new next hop;
+
+ - Any of the actions that can occur when the LSR receives a label
+ mapping from the FEC's new next hop.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - FEC. The FEC whose next hop changed.
+
+ - New Next Hop. The current next hop for the FEC.
+
+ - Old Next Hop. The previous next hop for the FEC.
+
+ - OldLabel. Label, if any, previously received from Old Next Hop.
+
+ - CurAttributes. The attributes, if any, currently associated with
+ the FEC.
+
+ - SAttributes. Attributes to be included in Label Label Request
+ message, if any, sent to New Next Hop.
+
+ Algorithm:
+
+ NH.1 Has LSR previously received and retained a label mapping for
+ FEC from Old Next Hop?
+ If not, goto NH.6.
+
+ NH.2 Remove label from forwarding/switching use. (See Note 1.)
+
+ NH.3 Is LSR using Liberal label retention?
+ If so, goto NH.6.
+
+ NH.4 Execute procedure Send_Message (Old Next Hop, Label Release,
+ OldLlabel).
+
+ NH.5 Delete label mapping for FEC previously received from Old
+ Next Hop.
+
+ NH.6 Has LSR previously received and retained a label mapping for
+ FEC from New Next Hop?
+ If not, goto NH.8.
+
+ NH.7 Generate Event: Received Label Mapping from New Next Hop.
+ Goto NH.11. (See Note 2.)
+
+ NH.8 Is LSR using Downstream on Demand advertisement? OR
+ Is Next Hop using Downstream on Demand advertisement? OR
+ Is LSR using Conservative label retention? (See Note 3.)
+ If so, goto NH.9. If not, goto NH.11.
+
+ NH.9 Execute procedure Prepare_Label_Request_Attributes (Next Hop,
+ FEC, CurAttributes, SAttributes)
+
+ NH.10 Execute procedure Send_Label_Request (New Next Hop, FEC, SAt-
+ tributes).
+ (See Note 4.)
+
+ NH.11 DONE.
+
+ Notes:
+
+ 1. If Label is not in forwarding/switching use, NH.2 has no
+ effect.
+
+ 2. If the LSR has a label for the FEC from the New Next Hop, it
+ should behave as if it had just received the label from the New
+ Next Hop.
+
+ 3. The purpose of the check on label retention mode is to avoid a
+ race with steps LMp.10-LMp.11 of the procedure for handling a
+ Label Mapping message where the LSR operating in Conservative
+ Label retention mode may have released a label mapping received
+ from the New Next Hop before it detected the FEC next hop had
+ changed.
+
+ 4. Regardless of the Label Request procedure in use by the LSR, it
+ must send a label request if the conditions in NH.8 hold.
+ Therefore it executes the Send_Label_Request procedure directly
+ rather than perform LSR Label Request procedure.
+
+A.1.7. Receive Notification / No Label Resources
+
+ Summary:
+
+ When an LSR receives a No Label Resources notification from an LDP
+ peer, it stops sending label request messages to the peer until it
+ receives a Label Resources Available Notification from the peer.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - FEC. The FEC for which a label was requested.
+
+ - MsgSource. The LDP peer that sent the Notification message.
+
+ Algorithm:
+
+ NoRes.1 Delete record of outstanding label request for FEC sent to
+ MsgSource.
+
+ NoRes.2 Record label mapping for FEC from MsgSource is needed but
+ that no label resources are available.
+
+ NoRes.3 Set status record indicating it is not OK to send label
+ requests to MsgSource.
+
+ NoRes.4 DONE.
+
+A.1.8. Receive Notification / No Route
+
+ Summary:
+
+ When an LSR receives a No Route notification from an LDP peer in
+ response to a Label Request message, the Label No Route procedure
+ in use dictates its response. The LSR either will take no further
+ action, or it will defer the label request by starting a timer and
+ send another Label Request message to the peer when the timer later
+ expires.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - FEC. The FEC for which a label was requested.
+
+ - Attributes. The attibutes associated with the label request.
+
+ - MsgSource. The LDP peer that sent the Notification message.
+
+ Algorithm:
+
+ NoNH.1 Delete record of outstanding label request for FEC sent to
+ MsgSource.
+
+ NoNH.2 Perform LSR Label No Route procedure.
+
+ For Request No Retry
+
+ 1. Goto NoNH.3.
+
+ For Request Retry
+
+ 1. Record deferred label request for FEC and Attributes
+ to be sent to MsgSource.
+
+ 2. Start timeout. Goto NoNH.3.
+
+ NoNH.3 DONE.
+
+A.1.9. Receive Notification / Loop Detected
+
+ Summary:
+
+ When an LSR receives a Loop Detected notification from an LDP peer
+ in response to a Label Request message, it behaves as if it had
+ received a No Route notification.
+
+ Context:
+
+ See "Receive Notification / No Route".
+
+ Algorithm:
+
+ See "Receive Notification / No Route"
+
+A.1.10. Receive Notification / Label Resources Available
+
+ Summary:
+
+ When an LSR receives a Label Resources Available notification from
+ an LDP peer, it resumes sending label requests to the peer.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - MsgSource. The LDP peer that sent the Notification message.
+
+ - SAttributes. Attributes stored with postponed Label Request mes-
+ sage.
+
+ Algorithm:
+
+ Res.1 Set status record indicating it is OK to send label requests
+ to MsgSource.
+
+ Res.2 Iterate through Res.6 for each record of a FEC label mapping
+ needed from MsgSource for which no label resources are avail-
+ able.
+
+ Res.3 Is MsgSource the next hop for FEC?
+ If not, goto Res.5.
+
+ Res.4 Execute procedure Send_Label_Request (MsgSource, FEC, SAttri-
+ butes). If the procedure fails, terminate iteration.
+
+ Res.5 Delete record that no resources are available for a label
+ mapping for FEC needed from MsgSource.
+
+ Res.6 End iteration from Res.2
+
+ Res.7 DONE.
+
+A.1.11. Detect local label resources have become available
+
+ Summary:
+
+ After an LSR has sent a No Label Resources notification to an LDP
+ peer, when label resources later become available it sends a Label
+ Resources Available notification to each such peer.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - Attributes. Attributes stored with postponed Label Mapping mes-
+ sage.
+
+ Algorithm:
+
+ ResA.1 Iterate through ResA.4 for each Peer to which LSR has previ-
+ ously sent a No Label Resources notification.
+
+ ResA.2 Execute procedure Send_Notification (Peer, Label Resources
+ Available)
+
+ ResA.3 Delete record that No Label Resources notification was previ-
+ ously sent to Peer.
+
+ ResA.4 End iteration from ResA.1
+
+ ResA.5 Iterate through ResA.8 for each record of a label mapping
+ needed for FEC for Peer but no-label-resources. (See Note
+ 1.)
+
+ ResA.6 Execute procedure Send_Label (Peer, FEC, Attributes). If the
+ procedure fails, terminate iteration.
+
+ ResA.7 Clear record of FEC label mapping needed for peer but no-
+ label-resources.
+
+ ResA.8 End iteration from ResA.5
+ ResA.9 DONE.
+
+ Notes:
+
+ 1. Iteration ResA.5 through ResA.8 handles the situation where the
+ LSR is using Downstream Unsolicited label distribution and was
+ previously unable to allocate a label for a FEC.
+
+A.1.12. LSR decides to no longer label switch a FEC
+
+ Summary:
+
+ An LSR may unilaterally decide to no longer label switch a FEC for
+ an LDP peer. An LSR that does so must send a label withdraw message
+ for the FEC to the peer.
+
+ Context:
+
+ - Peer. The peer.
+
+ - FEC. The FEC.
+
+ - PrevAdvLabel. The label for FEC previously advertised to Peer.
+
+ Algorithm:
+
+ NoLS.1 Execute procedure Send_Label_Withdraw (Peer, FEC, PrevAdvLa-
+ bel). (See Note 1.)
+
+ NoLS.2 DONE.
+
+ Notes:
+
+ 1. The LSR may remove the label from forwarding/switching use as
+ part of this event or as part of processing the label release
+ from the peer in response to the label withdraw.
+
+A.1.13. Timeout of deferred label request
+
+ Summary:
+
+ Label requests are deferred in response to No Route and Loop
+ Detected notifications. When a deferred FEC label request for a
+ peer times out, the LSR sends the label request.
+
+ Context:
+
+ - LSR. The LSR handling the event.
+
+ - FEC. The FEC associated with the timeout event.
+
+ - Peer. The LDP peer associated with the timeout event.
+
+ - Attributes. Attributes stored with deferred Label Request mes-
+ sage.
+
+ Algorithm:
+
+ TO.1 Retrieve the record of the deferred label request.
+
+ TO.2 Is Peer the next hop for FEC?
+ If not, goto TO.4.
+
+ TO.3 Execute procedure Send_Label_Request (Peer, FEC).
+
+ TO.4 DONE.
+
+A.2. Common Label Distribution Procedures
+
+ This section specifies utility procedures used by the algorithms that
+ handle label distribution events.
+
+A.2.1. Send_Label
+
+ Summary:
+
+ The Send_Label procedure allocates a label for a FEC for an LDP
+ peer, if possible, and sends a label mapping for the FEC to the
+ peer. If the LSR is unable to allocate the label and if it has a
+ pending label request from the peer, it sends the LDP peer a No
+ Label Resources notification.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the label mapping is to be sent.
+
+ - FEC. The FEC for which a label mapping is to be sent.
+
+ - Attributes. The attributes to be included with the label mapping.
+
+ Additional Context:
+
+ - LSR. The LSR executing the procedure.
+
+ - Label. The label allocated and sent to Peer.
+
+ Algorithm:
+
+ SL.1 Does LSR have a label to allocate?
+ If not, goto SL.9.
+
+ SL.2 Allocate Label and bind it to the FEC.
+
+ SL.3 Install Label for forwarding/switchng use.
+
+ SL.4 Execute procedure Send_Message (Peer, Label Mapping, FEC,
+ Label, Attributes).
+
+ SL.5 Record label mapping for FEC with Label and Attributes has
+ been sent to Peer.
+
+ SL.6 Does LSR have a record of a FEC label request from Peer
+ marked as pending?
+ If not, goto SL.8.
+
+ SL.7 Delete record of pending label request for FEC from Peer.
+
+ SL.8 Return success.
+
+ SL.9 Does LSR have a label request for FEC from Peer marked as
+ pending?
+ If not, goto SL.13.
+
+ SL.10 Execute procedure Send_Notification (Peer, No Label
+ Resources).
+
+ SL.11 Delete record of pending label request for FEC from Peer.
+
+ SL.12 Record No Label Resources notification has been sent to Peer.
+ Goto SL.14.
+
+ SL.13 Record label mapping needed for FEC and Attributes for Peer,
+ but no-label-resources. (See Note 1.)
+
+ SL.14 Return failure.
+
+ Notes:
+
+ 1. SL.13 handles the case of Downstream Unsolicited label distri-
+ bution when the LSR is unable to allocate a label for a FEC to
+ send to a Peer.
+
+A.2.2. Send_Label_Request
+
+ Summary:
+
+ An LSR uses the Send_Label_Request procedure to send a request for
+ a label for a FEC to an LDP peer if currently permitted to do so.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the label request is to be sent.
+
+ - FEC. The FEC for which a label request is to be sent.
+
+ - Attributes. Attributes to be included in the label request. E.g.,
+ Hop Count, Path Vector, CoS.
+
+ Additional Context:
+
+ - LSR. The LSR executing the procedure.
+
+ Algorithm:
+
+ SLRq.1 Has a label request for FEC previously been sent to Peer and
+ is it marked as outstanding?
+ If so, Return success. (See Note 1.)
+
+ SLRq.2 Is status record indicating it is OK to send label requests
+ to Peer set?
+ If not, goto SLRq.6
+
+ SLRq.3 Execute procedure Send_Message (Peer, Label Request, FEC,
+ Attributes).
+
+ SLRq.4 Record label request for FEC has been sent to Peer and mark
+ it as outstanding.
+
+ SLRq.5 Return success.
+
+ SLRq.6 Postpone the label request by recording label mapping for FEC
+ and Attributes from Peer is needed but that no label
+ resources are available.
+
+ SLRq.7 Return failure.
+
+ Notes:
+
+ 1. If the LSR is a non-merging LSR it must distinguish between
+ attempts to send label requests for a FEC triggered by dif-
+ ferent upstream LDP peers from duplicate requests. This pro-
+ cedure will not send a duplicate label request.
+
+A.2.3. Send_Label_Withdraw
+
+ Summary:
+
+ An LSR uses the Send_Label_Withdraw procedure to withdraw a label
+ for a FEC from an LDP peer. To do this the LSR sends a Label With-
+ draw message to the peer.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the label withdraw is to be sent.
+
+ - FEC. The FEC for which a label is being withdrawn.
+
+ - Label. The label being withdrawn
+
+ Additional Context:
+
+ - LSR. The LSR executing the procedure.
+
+ Algorithm:
+
+ SWd.1 Execute procedure Send_Message (Peer, Label Withdraw, FEC,
+ Label)
+
+ SWd.2 Record label withdraw for FEC has been sent to Peer and mark
+ it as outstanding.
+
+A.2.4. Send_Notification
+
+ Summary:
+
+ An LSR uses the Send_Notification procedure to send an LDP peer a
+ notificaction message.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the label withdraw is to be sent.
+
+ - Status. Status code to be included in the Notification message.
+
+ Additional Context:
+
+ None.
+
+ Algorithm:
+
+ SNt.1 Execute procedure Send_Message (Peer, Notification, Status)
+
+A.2.5. Send_Message
+
+ Summary:
+
+ An LSR uses the Send_Message procedure to send an LDP peer an LDP
+ message.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the message is to be sent.
+
+ - Message Type. The type of message to be sent.
+
+ - Additional message contents . . . .
+
+ Additional Context:
+
+ None.
+
+ Algorithm:
+
+ This procedure is the means by which an LSR sends an LDP message of
+ the specified type to the specified LDP peer.
+
+A.2.6. Check_Received_Attributes
+
+ Summary:
+
+ Check the attributes received in a Label Mapping or Label Request
+ message. If the attributes include a Hop Count or Path Vector, per-
+ form a loop detection check. If a loop is detected, send a Loop
+ Detected Notification message to MsgSource.
+
+ Parameters:
+
+ - MsgSource. The LDP peer that sent the message.
+
+ - RAttributes. The attributes in the message.
+
+ Additional Context:
+
+ - LSR Id. The unique LSR Id of this LSR.
+
+ - Hop Count. The Hop Count, if any, in the received attributes.
+
+ - Path Vector. The Path Vector, if any in the received attributes.
+
+ Algorithm:
+
+ CRa.1 Do RAttributes include Hop Count?
+ If not, goto CRa.5.
+
+ CRa.2 Does Hop Count exceed Max allowable hop count?
+ If so, goto CRa.6.
+
+ CRa.3 Do RAttributes include Path Vector?
+ If not, goto CRa.5.
+
+ CRa.4 Does Path Vector Include LSR Id? OR
+ Does length of Path Vector exceed Max allowable length?
+ If so, goto CRa.6
+
+ CRa.5 Return No Loop Detected.
+
+ CRa.6 Execute procedure Send_Notification (MsgSource, Loop
+ Detected)
+
+ CRa.7 Return Loop Detected.
+
+ CRa.8 DONE
+
+A.2.7. Prepare_Label_Request_Attributes
+
+ Summary:
+
+ This procedure is used whenever a Label Request is to be sent to a
+ Peer to compute the Hop Count and Path Vector, if any, to include
+ in the message.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the message is to be sent.
+
+ - FEC. The FEC for which a label request is to be sent.
+
+ - RAttributes. The attributes this LSR associates with the LSP for
+ FEC.
+
+ - SAttributes. The attributes to be included in the Label Request
+ message.
+
+ Additional Context:
+
+ - LSR Id. The unique LSR Id of this LSR.
+
+ Algorithm:
+
+ PRqA.1 Is Hop Count required for this Peer (see Note 1.) ? OR
+ Do RAttributes include a Hop Count? OR
+ Is Loop Detection configured on LSR?
+ If not, goto PRqA.14.
+
+ PRqA.2 Is LSR ingress for FEC?
+ If not, goto PRqA.6.
+
+ PRqA.3 Include Hop Count of 1 in SAttributes.
+
+ PRqA.4 Is Loop Detection configured on LSR?
+ If not, goto PRqA.14.
+
+ PRqA.5 Is LSR merge-capable?
+ If so, goto PRqA.14.
+ If not, goto PRqA.13.
+
+ PRqA.6 Do RAttributes include a Hop Count?
+ If not, goto PRqA.8.
+
+ PRqA.7 Increment RAttributes Hop Count and copy the resulting Hop
+ Count to SAttributes. (See Note 2.)
+ Goto PRqA.9.
+
+ PRqA.8 Include Hop Count of unknown (0) in SAttributes.
+
+ PRqA.9 Is Loop Detection configured on LSR?
+ If not, goto PRqA.14.
+
+ PRqA.10 Do RAttributes have a Path Vector?
+ If so, goto PRqA.12.
+
+ PRqA.11 Is LSR merge-capable?
+ If so, goto PRqA.14.
+ If not, goto PRqA.13.
+
+ PRqA.12 Add LSR Id to beginning of Path Vector from RAttributes and
+ copy the resulting Path Vector into SAttributes.
+ Goto PRqA.14.
+
+ PRqA.13 Include Path Vector of length 1 containing LSR Id in SAttri-
+ butes.
+
+ PRqA.14 DONE.
+
+ Notes:
+
+ 1. The link with Peer may require that Hop Count be
+ included in Label Request messages; for example, see
+ [ATM].
+
+ 2. For hop count arithmetic, unknown + 1 = unknown.
+
+A.2.8. Prepare_Label_Mapping_Attributes
+
+ Summary:
+
+ This procedure is used whenever a Label Mapping is to be sent to a
+ Peer to compute the Hop Count and Path Vector, if any, to include
+ in the message.
+
+ Parameters:
+
+ - Peer. The LDP peer to which the message is to be sent.
+
+ - FEC. The FEC for which a label request is to be sent.
+
+ - RAttributes. The attributes this LSR associates with the LSP for
+ FEC.
+
+ - SAttributes. The attributes to be included in the Label Request
+ message.
+
+ - IsPropagating. The LSR is sending the Label Mapping message to
+ propagate one received from the FEC next hop.
+
+ - PrevHopCount. The Hop Count, if any, this LSR associates with the
+ LSP for the FEC.
+
+ Additional Context:
+
+ - LSR Id. The unique LSR Id of this LSR.
+
+ Algorithm:
+
+ PMpA.1 Is Hop Count required for this Peer (see Note 1.) ? OR
+ Do RAttributes include a Hop Count? OR
+ Is Loop Detection configured on LSR?
+ If not, goto PMpA.19.
+
+ PMpA.2 Is LSR egress for FEC?
+ If not, goto PMpA.4.
+
+ PMpA.3 Include Hop Count of 1 in SAttributes. Goto PMpA.19.
+
+ PMpA.4 Do RAttributes have a Hop Count?
+ If not, goto PMpA.6.
+
+ PMpA.5 Increment RAttributes Hop Count and copy the resulting Hop
+ Count to SAttributes. See Note 2. Goto PMpA.7.
+
+ PMpA.6 Include Hop Count of unknown (0) in SAttributes.
+
+ PMpA.7 Is Loop Detection configured on LSR?
+ If not, goto PMpA.19.
+
+ PMpA.8 Do RAttributes have a Path Vector?
+ If so, goto PMpA.17.
+
+ PMpA.9 Is LSR propagating a received Label Mapping?
+ If not, goto PMpA.18.
+
+ PMpA.10 Does LSR support merging?
+ If not, goto PMpA.12.
+
+ PMpA.11 Has LSR previously sent a Label Mapping for FEC to Peer?
+ If not, goto PMpA.18.
+
+ PMpA.12 Do RAttributes include a Hop Count?
+ If not, goto PMpA.19.
+
+ Res.13 Is Hop Count in Rattributes unknown(0)?
+ If so, goto PMpA.18.
+
+ PMpA.14 Has LSR previously sent a Label Mapping for FEC to Peer?
+ If not goto PMpA.19.
+
+ PMpA.15 Is Hop Count in RAttributes different from PrevHopCount ?
+ If not goto PMpA.19.
+
+ PMpA.16 Is the Hop Count in RAttributes > PrevHopCount? OR
+ Is PrevHopCount unknown(0)
+ If not, goto PMpA.19.
+
+ PMpA.17 Add LSR Id to beginning of Path Vector from RAttributes and
+ copy the resulting Path Vector into SAttributes. Goto
+ PMpA.19.
+
+ PMpA.18 Include Path Vector of length 1 containing LSR Id in SAttri-
+ butes.
+
+ PMpA.19 DONE.
+
+ Notes:
+
+ 1. The link with Peer may require that Hop Count be included in
+ Label Mapping messages; for example, see [ATM].
+
+ 2. For hop count arithmetic, unknown + 1 = unknown.